Multilayer film for label and a method for providing such

ABSTRACT

The invention relates to providing a method for obtaining a multilayer film for thermally inducible shrink labels, products thereof and use of such products.

FIELD OF THE INVENTION

The application relates to a plastic film. In particular, theapplication relates to a shrinkable plastic film for labellingapplications. The application concerns further a method for providing ashrinkable plastic film for labelling applications.

BACKGROUND OF THE INVENTION

It is general practice to apply a label to a surface of an item toprovide decoration, and/or to display information about the productbeing sold, such as the content of the item, a trade name or logo. Inaddition to pressure-sensitive, wet glue and wrap around labels, otherlabelling technologies are available, for example shrink sleeves. Shrinksleeves may be provided by forming a tube of plastic film, which may bedropped over an item to be labelled and subsequently fed the itemthrough a shrink-tunnel at elevated temperature causing the film toshrink and fit the shape of the item.

SUMMARY OF THE INVENTION

An object of the invention is to provide monoaxially stretchedmultilayer film structures and compositions having improved propertiesfor the labeling and recyclability. An object of the invention is toprovide a method for manufacturing monoaxially stretched multilayer filmstructures and compositions having improved properties for the labelingand recyclability.

Due to increasing environmental awareness, plastic materials and itemssuch as plastic containers and consumer bottles are recycled inincreasing amounts. To facilitate the recyclability of these items,materials used for labeling such items should be compatible with thegeneral recycling methods. One of the major recycling methods is basedon separation of the labels from the container to improve the purity ofthe recyclable plastic container material. In particular, the usedcontainers comprising labels may be shredded and washed to remove thelabels, which may comprise printing inks and various other impurities,such as adhesives. Novel labeling methods, such as heat-shrinked labels,shrink sleeves and roll-fed shrink sleeves, provide ways to reduce theuse of adhesives and improve the segregation of the labels from thecontainers. Therefore, it is desirable to obtain films used forlabeling, which may comprise a relatively low thermally inducedshrinkage in temperatures during transportation, where the temperaturemay rise up to 60° C., but a high thermally induced shrinkage in highertemperatures used in manufacturing of labels, such as labels used asroll-fed shrink labels (RFS). Furthermore, the films should be suitablefor disposable labels, printable to convey product information andeasily separable from the labeled articles, such as plastic containersor bottles.

Copolymers of alpha-olefin and alkyl acrylate have in general been usedas in the tie layer of a polymer film, in concentrations ranging between1 to 2% by weight. However, it has now been surprisingly been found outthat at least certain acrylate copolymers may in addition be suitablefor core layer polymers of thermally inducible multilayer films. Thecore layer of a multilayer film may thus comprise a copolymer ofalpha-olefin and alkyl acrylate. The various embodiments of theinvention relate to obtaining monoaxially stretched multilayer filmstructures and compositions having improved properties for the labelingand recyclability.

According to an aspect of the invention, there is provided a multilayerfilm for labeling comprising a first skin layer, a second skin layer anda core layer between the first skin layer and the second skin layer,wherein the core layer comprises copolymer of ethylene and butylacrylate, and wherein at least one of the first skin layer and thesecond skin layer comprises propylene terpolymer.

According to another aspect of the invention, there is provided a methodfor obtaining a multilayer film for thermally inducible shrink labels,the method comprising:

-   -   providing a first skin layer and a second skin layer, wherein at        least one of the first skin layer and the second skin layer        comprises propylene terpolymer,    -   providing a core layer comprising copolymer of ethylene and        butyl acrylate between the first skin layer and the second skin        layer,    -   stretching the multilayer film in the range of 4 to 7 times in a        first direction for obtaining a monoaxially stretched multilayer        film having a tension in the first direction, and    -   cooling the multilayer film to room temperature

A product according to an embodiment of the invention may be used forexample as a label on a container surface, wherein the container may be,for example, a recyclable plastic bottle, such as a PET bottle. Inparticular, the film may be used for a shrink sleeve, wherein the filmis first processed into a label having defined dimensions andorientation, which label may then be attached against a containersurface by thermally induced shrinking, preferably on a temperature inthe range of 65° C. to 85° C., more preferably in the range of 70° C. to85° C., most preferably in the range of 70° C. to 80° C. By selectingthe composition and the structure of the film, a desirable shrinkage,such as at least 15% or at least 25%, preferably at least 35% may beobtained. The composition and the structure of the film may also beselected to control the stiffness of the film, which may be needed forthe label manufacturing and disposing processes. Furthermore, thecomposition has an effect to the printability, which may be needed on atleast one skin surface. In particular, the density of the film materialmay be less than the density of the container material and water usedfor washing, such that the label material may float and can thus beseparated from sinking container material by skimming the surface.

Further embodiments of the invention are presented in the detaileddescription of the invention and in the dependent claims.

DESCRIPTION OF THE DRAWINGS

In the following some examples and embodiments of the invention will bedescribed in more detail with reference to appended drawings, in which

FIG. 1 shows, in a cross sectional view, an example embodiment of amultilayer plastic film face stock structure for a label,

FIG. 2 shows examples for shrinkage for embodiments of heat shrinkablelabel films according to the present invention,

FIG. 3 shows examples for relative shrinkage for embodiments of heatshrinkable label films according to the present invention,

FIG. 4 illustrates an embodiment of the free shrinkage potential of amonoaxially stretched multilayer film,

FIG. 5 shows an example embodiment of a thermally induced shrinkage of alabel,

FIG. 6 shows an example embodiment of a label shrunk and fitted on asurface of an item i.e. a labelled item.

DETAILED DESCRIPTION OF THE INVENTION

In this description and claims, the percentage values relating to anamount of raw materials are percentages by weight (wt. %) unlessotherwise indicated.

The films of the invention are suitable for labels and use for labellingof items. Especially the multilayer plastic films may be used for a facefilm of a label. In other words, the films described above are suitablefor a label film. The films are suitable for labelling of a wide rangeof product designs and particularly suitable for highly contouredcontainers and products comprising curved sections, recesses and/orprotrusions at the outer surface. The labels comprising heat shrinkmultilayer face film are suitable for items of glass, plastic, ceramics,glass, and metal. Shrinkage properties of films and/or labels enablelabels to be used in highly contoured containers. The item may compriseor consists of polyethylene terephthalate (PET). The item may have ashape of a bottle. The films of the invention may also be used forlabelling of batteries. The films may also be used as a face stock of alabel laminate further comprising an adhesive layer and a release liner.For example, film according to the some or/all embodiments may be usedfor a face stock of a wash-off labels. Wash-off labels may be used e.g.for labelling of glass bottles. Due to the shrinking capability of thefilm, the labels may be efficiently detached and removed (washed-off)from the surface labelled during subsequent washing process.

As used herein, the phrase “label” refers to a piece of material, whichis used for labelling of an item. Label may be used to identifysomething. Label may be attached to an article. In other words, label issuitable to be applied to a surface of an item to provide decoration,and/or to display information about the product being sold, such ascontent information, a trade name, a logo, a barcode, or any othergraphics. The item may also be called as an article, or a substrate.Preferably, the label comprises a face film and at least some graphicson a surface of the face film. A face film may also be referred to as alabel film. The graphics may comprise, for example, printed informationand/or decoration. The graphics may comprise, for example one or morecolours. A label may be a product having length, width and thickness,the product being a film or derived from a film, for example by cutting.A label comprises a first surface portion intended to be attached to asecond surface portion different from the first surface portion. Thesecond surface portion may be a separate surface portion of the label,or a surface portion of another product. The first and second surfaceportions may be adjoined to each other by various means, such as byusing an adhesive, a solvent or heat. For example, the first and thesecond surface portions may be adjoined to each other by adhesive, whenthe label is attached on the surface of an item to be labelled, such asa container. Alternatively, or in addition, a first surface portion ofthe label may be seamed to another surface portion of the same label,when the label is produced as a sleeve to be fitted around the outersurface of a container to be labelled.

As used herein, the phrase “shrinkable” refers to a property of aplastic film or a label made thereof to shrink under exposure toexternal energy. A thermally shrinkable plastic film or a heatshrinkable plastic film, such as a face film of a label, may shrink whenexposed to an elevated temperature. The exposure to an elevatedtemperature may induce a shrinkage. Heat may be applied by variousmeans, such as by long wavelength radiation, steam, hot air or by anycombination of these. Long wavelength radiation may be, for example,infra-red range radiation. In response to application of heat, thethermally inducible shrinkable plastic film or a label comprising saidplastic film is arranged to shrink.

As used herein, the phrase “machine direction” MD refers to the runningdirection S_(x), of the plastic film or continuous label web duringlabel manufacturing. “Transverse direction” TD or “cross direction” CDrefers to the direction S_(y) perpendicular to the running directionS_(x) of the film or label web.

A ratio of total film thickness before and after stretching is called a“draw ratio” or “drawing ratio” (DR). It may also be referred to as astretching ratio or orientation ratio. In other words, draw ratio is anon-oriented (undrawn) film thickness in relation to the oriented(drawn) film thickness. The non-oriented film thickness is the thicknessafter extrusion and subsequent chilling of the film. When stretching thefilm, the thickness of the film may diminish in the same ratio as thefilm stretches or elongates. For example, a film having thickness of 100micrometers before uniaxial orientation is stretched by a draw ratio of5. After the uniaxial orientation the film may have a fivefolddiminished thickness of 20 micrometers.

The plastic film may be drawn (stretched) at least in one direction. Thefilm may be drawn in a machine direction, in a transverse direction, orboth. The resulting film is thus monoaxially (uniaxially) oriented (MO)or biaxially oriented (BO). Monoaxially oriented film may be machineoriented (MDO) or transverse oriented (TDO) in accordance to thedirection of the orientation (stretching). The stretching of the filmand orientation of the polymer chains may be observed microscopically.Further, the orientation is detectable e.g. from the mechanicalproperties of the films, such as values of modulus and/or tensilestrength.

As used herein, the phrase “roll-fed shrink film” (RFS) refers tolabelling process, where a ready cut label is rolled over a containerand then the label is shrunk in order to conform shape and size of thecontainer. Label is supplied from a reel, cut into individual labels andapplied around an item. Adhesive (e.g. hot melt adhesive) is used tohold the label on the surface of the item. The adhesive may be appliedon the label or on the container in an area between the leading edge andthe surface of the container. The adhesive may also be applied betweentrailing and leading edges of the label. When rolled over to an item,the trailing and leading edges may overlap and form a seam. Subsequentshrinking process at high temperatures enables tight fitting of thelabel around the item. Heat shrinking may occur at a shrink tunnel,where for example hot air, steam, infra-red radiation or a combinationof any of these may be blown towards passing items. The describedprocess may be called as on-line labelling process. Roll-fed shrinkfilms may be monoaxially oriented in machine direction (MD).Alternatively, films may be monoaxially oriented in transversedirection. When a label consists of a MDO shrink film as a face stock,and the machine direction of the label extends circumferentially aroundthe item, the label is arranged to shrink primarily in the orientationdirection when heated. In addition to the above described “roll-fedshrink film” (RFS), variations of the labelling process exist. Forexample, in some labeling applications the label may be hold on top ofthe bottle without an adhesive, such as a hot melt adhesive. In suchapplications, a sleeve label may be wound and cut on a cylindricalmandrel having vacuum inside to hold the sleeve on correct position. Asin the roll-fed shrink film application, there may be a small overlap ofsleeve label ends, which may be seamed, for example, with laser weldingor ultrasonic radiation, to create a label sleeve. Then sleeve may bepositioned on top of a container and subsequently shrunk on top of thecontainer in a steam tunnel.

As used herein, the phrase “shrink-sleeve” or “heat shrinkable sleevefilm” (HS) refers to a labelling process, where a preformed label tube(or sleeve) is introduced around an item. Shrink sleeve label comprisesor consists of transverse direction oriented (TDO) shrink film. The filmis seamed into a continuous tube label around the axis extending to themachine direction (S_(x)). The formed continuous tube (or sleeve) is cutinto predetermined lengths and supplied as a form of individual tubelabel around an item. The item or container may be warmed before acylindrical tube label is introduced over it. Tube around an item isheated in order to shrink the tube label around the item. The transversedirection orientation of the tube label extends circumferentially aroundthe item. Thus, the label may primarily shrink in the transversedirection.

Multilayer Structure

FIG. 1 presents a cross sectional view of a multilayer film 100according to an example of the invention. A multilayer film 100 refersto a film structure comprising a plurality of layer, such as two or morelayers. Preferably, a multilayer film 100 suitable for shrink labelscomprises a symmetrical structure, wherein a core layer 130 having afirst surface 131 and a second surface 132 is directly adhered from bothsurfaces 131, 132 to other layers of the film. The core layer 130 may beadjacent to a first skin layer 110 and a second skin layer 120, whereinthe phrase “skin layer” refers to any layer of the multilayer film 130having only one of its principal surfaces directly adhered to anotherlayer of the multilayer film 100. The inner surfaces 112, 122 of thefirst skin layer 110 and the second skin layer 120 are adhered againstanother layer of the multilayer film 100, such as the core layer 130.The other principal surfaces of each of the two skin layers form theouter surfaces 111, 121 of the first skin layer 110 and the second skinlayer 120, and the outer surfaces of the multilayer film 100. The outersurface of the multilayer film 100 may be used for printing, such asgraphics or text, to carry information on a label.

In addition to the core layer 130 and the skin layers 110, 120, themultilayer film 100 may comprise additional layers between the two skinlayers 110, 120. When the multilayer film 100 is intended to bethermally shrinkable, the multilayer film 100 may comprise a symmetricalstructure, in other words, there is an equal number of layers on bothsides of the core layer 130. In particular, symmetrical structureswherein the thickness d110, d120 of the skin layers 110, 120 compriseequal thickness, may have less tendency for curling. The curlingtendency may be apparent even before there is any shrinking, in someasymmetric films in particular. For example, in some asymmetric filmscurling may be due to the different compositions and layer thicknesses.The curling refers to one surface of the multilayer film 100 deformingmore than the other surface. Symmetrical multilayer film 100 structuresmay in particular be used to improve the thermally inducible shrinkageof labels, wherein the skin layers 110, 120 may comprise similarcompositions.

The multilayer film 100 may comprise a thickness d1, comprising thethickness d130 of the core layer and the thickness d110 of the firstskin layer and the thickness d120 of the second skin layer. In general,the core layer may have the largest thickness d130, such as 60%, 70%,80%, 90% or 95% of the thickness d1 of the multilayer film 100.Furthermore the thickness profile of the multilayer film may besymmetrical, such that the thickness d110 of the first skin layer may beequal to the thickness d120 of the second skin layer. The thicknessd110, d120 of a skin layer 110, 120 may be, for example 2.5%, 5%, 10%,15% or 20% of the thickness d1 of the multilayer film 100. The corelayer 130 may form major portion of the multilayer film 100 structure.The core layer 130 may have a monolayer or multilayer structure. Thecore layer 130 may be thicker than the first skin layer 110 and thesecond skin layer 120. For example, the core layer 130 may form 60% ofthe total thickness d1 of the multilayer structure. Alternatively, thecore layer 130 may have thickness d130 of 40% of the total thickness d1of the multilayer film 100. In a symmetric multilayer film 100comprising three layers, the core layer 130 having thickness d130 of 40%of the total thickness d1 of the multilayer film 100 still forms majorportion of the multilayer film 100, since the skin layers 110, 120 mayhave thickness d110, d120 of up to 30% of the multilayer film 100thickness d1. In other words, the thickness of the first skin layer orthe second skin layer may be equal to or less than 30% of the totalthickness of the multilayer film 100. Thickness d130 of the core layer130 may be from 15 to 50 microns, or from 20 to 50 microns, preferablyaround 30 or 25 microns. Thickness of skin layers d110, d120 may be 40%of the total thickness d1 of the multilayer structure. Alternatively,the combined thickness of skin layers 110 and d120 may be 60% of thetotal thickness d1. The thickness d110, d120 of a skin layer 110,120 maybe less than 20 microns, preferably around 10 or 7.5 microns or less.The overall thickness d1 of the multilayer film 100 may be from 20 to 70microns or from 25 to 60 microns, preferably around 50 microns or around40 microns or less. Preferably the multilayer film 100 has uniformoverall thickness. Uniform thickness refers to a homogeneous thicknessof a multilayer film 100, wherein a thickness variation along themultilayer film 100 is small. For example in a multilayer film 100 areaof 100 mm times 100 mm variation of the film thickness is less than 10%,preferably between 0.1 and 5.0%. Uniform thickness of the multilayerfilm 100 provides better quality labels, for example, labels having goodvisual appearance. Uniform multilayer film 100 thickness may have effecton the register control and image quality of the printing.

Stretching

Unoriented multilayer film 100 may be manufactured by using either acast or blown-film extrusion process. A shrinkable multilayer film 100may be obtained by stretching (drawing) the extruded multilayer film 100to an extent several times its original dimension to orient themultilayer film 100. The stretching may be performed by using heateddraw rolls with gradually increasing speed. The stretching may beperformed below the melting temperature of the polymer. Furthermore, thestretching may be performed at or near the glass transition temperatureof the polymer. Preferably the multilayer film 100 stretchingtemperature is between 50 and 120° C., preferably between 60 and 110° C.or between 60 and 100° C. The stretching of the multilayer film 100 isperformed at the lowest possible temperature, which in general is atemperature slightly, in the range of 5 to 15° C. above the glasstransition temperature of the multilayer film 100. As a rule of thumb,the stretching is done on a film which remains transparent or clearduring the stretching procedure.

The stretching may be performed in one direction of the film, e.g. inmachine direction, i.e. in longitudinal direction of the multilayer film100. Multilayer film 100 stretched in machine direction may be referredto as machine direction oriented (MDO) multilayer film 100. In MDOmultilayer film 100 the polymer chains are oriented monoaxially in saidmachine direction. Machine direction oriented multilayer film 100 may beused for roll-fed labelling, i.e. in a labelling process where themultilayer film 100 is supplied from a reel, cut into separate labels,after which labels are mounted around an item and seamed duringlabelling step using adhesive, such as UV-acrylic hot-melt adhesive.Alternatively seam may be formed by solvent seaming, hot-bar(heat-sealing), laser-welding or ultrasonic radiation. During mountingthe label around an item some adhesive may be used between the label andthe surface of the item in order to keep the label in specified place.The label around the item may be shrunk in order to form a tightattachment and/or to conform to the shape of the item.

Alternatively, the multilayer film 100 may be stretched in transversedirection (TD), which means the direction perpendicular to machinedirection of the film. Transverse direction (TD) may be referred also toas cross direction (CD). Transverse oriented films may be used forshrink-sleeve type of labels, which films are seamed into a form of atube prior to labelling, in general by using a solvent. The tube is cutinto tubes of predetermined lengths and supplied as in a form of tubearound an item. The labelled item may be heated in order to provideshrinking of the film around the item and/or to provide tight fitting ofthe label around the item and/or to conform the shape of the item withthe label.

The stretched (oriented) structure of the multilayer film 100 andorientation of the polymer chains may be observed microscopically.Further, the orientation is detectable e.g. from the mechanicalproperties of the films, such as values of modulus and/or tensilestrength.

The multilayer film 100 may be monoaxially stretched approximately from2 to 10 times, preferably 3 to 9 times, and most preferably from 3 to 8times in a first direction. The multilayer film 100 may be monoaxiallystretched in machine direction. Draw ratio (or orientation ratio) of theMD film is from 2 to 10 (from 2:1 to 10:1), preferably from 3 to 9 (from3:1 to 9:1), most preferably from 3 to 8 (from 3:1 to 8:1),correspondingly. Alternatively, the multilayer film 100 may bemonoaxially stretched in transverse direction, for example, from 2 to 10times, preferably 3 to 9 times, and most preferably from 3 to 8 times.

For example, the multilayer film 100 may be oriented at least 3 times atleast in one direction, i.e. the draw ratio (stretching ratio) of thefilm is at least 3 in one direction of the film. Alternatively, theorientation ratio at least in one direction may be at least 4. Forexample, the draw ratio may be in the range of 3 to 7, preferably in therange of 4 to 6. A stretching of at least 3 times may be beneficial toprovide sufficient shrinkage potential for the film. A higher stretchingfacilitates the formation of sufficient shrink tension to hold the labelin place against an object. However, a high stretching also increasesthe risk of the multilayer film 100 breaking or snapping duringstretching. The breaking of the multilayer film 100 is related to thestretching conditions. In particular, the layer compositions may beselected to adjust the stretching and shrinking behaviour of amultilayer film 100. In compositions according at least someembodiments, a stretching equal to or less than 7 times, such as equalto or less than 6 times is preferable.

After stretching, the multilayer film 100 may be cooled with one or morecooling rolls having temperature of less than in the multilayer film 100stretching. Shrinkage potential may be provided for the multilayer film100, by rapidly cooling the multilayer film 100 after the stretching.The temperature profile in cooling may be decreasing. In other words,one or more cooling rolls may have a decreasing temperature profilestarting at or slightly below stretching temperature, each subsequentroll having a temperature equal to or less than the previous coolingroll. By subsequent cooling after stretching, the multilayer film 100 isnot heat set, i.e. not annealed, which increases the shrinkage potentialfor the multilayer film 100. The cooling may be arranged by passing themultilayer film 100 through cooling rolls. Cooling of the film may begradual, for example first cooling roll(s) may have a temperature ofaround 90° C., for example in the range of 80 and 90° C. Subsequentcooling roll(s) may have temperature equal to or less than the previouscooling roll, such as in the range of 90° C. to 25° C., or in the rangeof 50° C. and 25° C. The cooling rolls at the end of the cooling stepmay comprise a temperature in the range of 10° C. and 20° C., or around25° C. such that the multilayer film 100 temperature may be diminishedto a general room temperature in the range of 22° C. to 25° C.Stretching and subsequent cooling may provide suitable shrink potentialfor the multilayer film 100. Due to the shrink potential, the orientedmultilayer film 100 comprise an ability to shrink under elevatedtemperatures above an initial shrinkage temperature towards the originalunstretched dimensions. In other words, subsequent application ofsufficient heat causes the multilayer film 100 comprising thermallyinducible shrinkage potential to relax and the multilayer film 100 mayreturn at least to some extent from the oriented state towards thenon-oriented (initial) state. Thus, machine direction oriented filmsprimarily shrink in the machine direction and transverse oriented filmsin the transverse direction.

The multilayer film 100 may be stretched, for example monoaxially in alinear direction DIR1 to orientate the multilayer film 100 in machinedirection or transverse direction. The term “machine direction” MDrefers to the running direction Sx of the multilayer film 100 duringmanufacturing and “transverse direction” TD or “cross direction” CDrefers to the direction Sy perpendicular to the running direction Sx ofthe multilayer film 100. During stretching the randomly oriented polymerchains of the cast or extruded multilayer film 100 are oriented in thedirection of stretching, also denoted as drawing. The degree oforientation of the polymer chains depends on the stretching ratio of themultilayer film 100. In other words, the polymer chains in themultilayer film 100 stretched with a higher draw ratio are more orientedwhen compared to a multilayer film 100 stretched with lower draw ratio.In general, a multilayer film 100 may be stretched by a given ratio toobtain desired mechanical, thermodynamic and optical properties for themultilayer film 100. Furthermore, after stretching, the orientedmultilayer film 100 may be slitted, referring to trimming thetransversal ends of the film, to obtain a multilayer film 100 comprisinga desired thickness d1. The desired thickness for a multilayer film 100prior to stretching may be, for example, in the range of 150 to 250micrometers (μm), such as 160, 180, 200, 220 or 240 micrometers (μm).According to an embodiment of the invention, the multilayer film 100 maybe stretched in the range of 4 to 7 times, preferably in the range of 4to 6 times, in a first direction DIR1. The first direction DIR1 may beparallel to the multilayer film machine direction. Alternatively, thefirst direction DIR1 may be perpendicular to the multilayer film machinedirection. When the multilayer film 100 is used for labels oriented inmachine direction, the labels may be printed, fed and cut directly froma roll, such as roll-fed shrink labels. When the multilayer film 100 isused for labels oriented in transverse direction, a separate step may berequired to first cut the film to a tubular shape, seam the tube andthen, prior to labelling, cut the individual tubes and apply these overthe container to be labeled. In other words a sleeve with a certainheight suitable to container/bottle may be cut just before sleeve isdropped around a container to be labelled.

The stretching reduced the thickness d1 of the film by the stretchingratio. The stretching ratio is the total film thickness d1 before andafter stretching, also denoted as “draw ratio” or “drawing ratio” (DR).In other words, stretching ratio is a ratio of non-oriented (undrawn)film thickness to the oriented (drawn) film thickness. The non-orientedfilm thickness is the thickness after casting or extrusion andsubsequent chilling of the film. When stretching the multilayer film100, the thickness of the multilayer film 100 may diminish in the sameratio as the multilayer film 100 length stretches or elongates. Forexample, a multilayer film 100 having a thickness of 100 micrometersbefore machine direction orientation (MDO) is stretched by a draw ratioof 5. After the machine direction orientation the facestock has afivefold diminished thickness of 20 micrometers. A thickness d1 for amultilayer film 100 after stretching may be, for example, in the rangeof 20 to 60 micrometers (μm) after monoaxially stretched and slitted.The range may preferably be in the range of 25 to 50 micrometers (μm),such as 25, 30, 35, 40, 45 or 50 micrometers (μm). The thicknessinterval in the range of 20 to 60 micrometers (μm) may be selected on amicrometer basis such that, for example in the range of 40 to 45micrometers (μm), the thickness d1 for a multilayer film 100 afterstretching may be 40, 41, 42, 43, 44 or 45 micrometers. The thickness d1may be measured from multiple, such as at least 3 or 4 or 5, separatelocations as an average thickness d1 of the multilayer film 100 afterslitting the multilayer film 100 ends from the stretched film. Thethickness d1, as well as the thickness d110, d120 and d130 of the corelayer 130, the first skin layer 110 and the second skin layer 120 of themultilayer film 100 may be selected based on the chemical composition ofthe layers. In particular, a layer composition providing increasedstiffness for the multilayer film 100, and in particular to the skinlayers 110, 120, may be used to reduce the thickness d1 of themultilayer film 100.

Thermal Shrinkage

Of particular interest are the thermodynamic properties of a monoaxiallystretched film. The stretching ratio providing the multilayer filmthickness d1 may be selected to adjust the shrinkage behavior of themultilayer film 100 in different dimensions Sx, Sy, Sz. In general,stretching has an effect on characteristics such as tensile strength,stiffness, tear resistance, and impact strength of the multilayer film100. When stretching a multilayer film 100 and cooling the film withoutannealing, for example by using a series of chilling rolls, eachsubsequent roll having a temperature equal to or less than the previousone, internal stresses are locked into the film. These internal stressescause shrink tension, which may be released by heating the film.

Shrinkage may be measured according to the following method: providing asample with measured and marked 100 mm times 100 mm area, placing thesample for 15 seconds to the water baths having temperatures atintervals of 5° C. from 55° C. to 98° C., cooling the sample at waterbath having temperature of around room temperature, drying the sampleand measuring the dimensions of the marked area of the sample.Preferably at least 3 or more parallel samples are used. Shrinkage isdetermined as the relative change of dimensions. The term “shrinkage” isdefined with reference to the method. In many labelling applications asteam tunnel may be preferred, to provide an easy method for uniformtransfer of heat. However, it is evident, and has been noticed, that thesame shrinkage properties apply regardless of the method, provided thatthe same temperatures are used. The composition of heat transfer medium(air, steam, water) is not critical for shrinkage behaviour.

The shrinkage potential and shrinkage behavior are further related tothe multilayer film layer compositions, structures and processingtechniques employed to manufacture the multilayer film 100. For example,different polymer compositions in a multilayer film layers may be usedto obtain a specific shrinkage curve in the principal direction ofshrinking. The principal shrinkage is due to the relaxation of thepolymer chains in a direction parallel to the stretching. However, thelinear distance of the label in a second direction DIR2 perpendicular tothe first direction DIR1 may change to conform to the shape of thelabeled item.

The thermally induced shrinkage may be focused on a local area or to thewhole plastic film area. When providing a heat shrink film or heatshrink label, the multilayer film may comprise stiffness. In general, amultilayer film, or a label obtained from a multilayer film, or a heatshrink label obtained from a multilayer film may be attached directly ona container surface by an adhesive prior to labelling. The adhesive maybe applied as a hot melt adhesive, for example by rolls or by sprayingone, two or more droplets of adhesive material on the surface of thecontainer to be labelled or on the item used for labelling. The labelmay then be wrapped or tightened against the container, and consequentlyseamed in place. The seaming may comprise the use of a solvent, or anadhesive, such as a ultra-violet (UV) radiation curable hot meltadhesive.

In the following description of shrinkage the following denotations areused:

-   h1 a first length of a label film prior to shrinking,-   w1 a second length of a label film prior to shrinking,-   d1 thickness of a label film prior to shrinking,-   L₀ a length of a film, in a first direction, before heat treatment,    wherein the first direction is in the plane of the film,-   L(T) the length of the part of the film having the length L₀ in the    first direction before heat treatment, after a heat treatment, in    which the temperature of the thermally shrinkable plastic film has    been T, and cooled back to the temperature before the heat    treatment. Thus, the length L(T) refers to a length of the shrunk    film,-   ε strain (when positive) or shrinkage (when negative),-   ε(T) shrinkage of a film, after a heat treatment wherein the    temperature of the thermally shrinkable plastic film has been T,    defined as ε(T)=[L(T)−L]/L. For thermally shrunk materials ε(T)<0;    in addition ε(T)>−1,-   ε(98° C.) shrinkage of a film, after a heat treatment wherein the    temperature of the thermally shrinkable plastic film has been 98°    C.,-   ε_(r)(T) relative shrinkage of a film, defined as ε(T)/ε(98° C.),-   pp percentage point, i.e. the absolute difference of relative values    given in per cents.

The shrinkage ε(T) for the temperature T is defined as the relativechange in length in the first direction; i.e. ε(T)=(L(T)−L₀)/L₀. It isnoted that by this definition, the numerical value of shrinkage isnegative, while the numerical value of strain would be positive. Thus a“better” shrinkage is, in terms of numbers, a more negative (i.e. asmaller) value. As is implicitly clear, in practical applications athermally shrinkable film can be shrunk using different heat sourcessuch as hot air, hot gas, steam, and/or radiation. Thus, in practice,drying is not necessarily needed.

In FIG. 2, the shrinkage curves of different samples according toembodiments of the invention are shown; with the reference “Samples”. Intotal 21 samples were manufactured and measured.

The values of relative shrinkage of different samples according toembodiments of the invention are shown in FIG. 3 with the reference“Samples”. In total 21 samples were manufactured and measured.

Referring to FIGS. 2 and 3, the film should use most of its shrinkagepotential for a reasonable small temperature change. To more preciselydefine the shrinkage potential, a relative temperature dependentshrinkage ε_(r)(T) is herein defined as ε_(r)(T)=ε_(r)(T)/ε(98°C.)={[L(T)−L₀]/L₀}/ε(98° C.). In this description, the value of ε_(r)(T)will be given in percentages. The reason for selecting the referencetemperature of 98° C. is that such a temperature is achievable using hotwater or unpressurized (pressure equals 1 atm) steam. It is noted thatthe film may shrink also for temperatures above 98° C., however theseare of little practical interest, since the films are commonly heated bywater and/or steam. So, the value ε(98° C.) is not a maximum shrinkage,only a reference value.

When the film uses most of its shrinkage potential for a reasonablesmall temperature change, the difference ε_(r)(T₂)−ε_(r)(T₁), betweenthe values of the relative temperature dependent shrinkage ε_(r)(T) forat least one pair of two temperatures T₂ and T₁, the temperatures havinga difference T₂−T₁=15° C., is more than 50 percentage points (pp);wherein the lower of the two temperatures, T₁, is from 65° C. to 70° C.For example, the lower of the two temperatures, T₁, may be 65° C.,whereby ε_(r)(80° C.)−ε_(r)(65° C.) is more than 50 pp. For example, thelower of the two temperatures, T₁, may be 70° C., whereby ε_(r)(85°C.)−ε_(r)(70° C.) is more than 50 pp. Preferably, the difference betweenthe values of the relative temperature dependent shrinkage ε_(r)(T) forat least the pair of temperatures T₂=85° C. and T₁=65° C., i.e.ε_(r)(T₂)−ε_(r)(T₁), is more than 65 pp; preferably more than 70 pp.

In addition or alternatively to the shrinkage ε(T), the shrinkagebehavior can be described using the relative shrinkage ε_(r)(T) asdefined above. In addition or alternatively to the shrinkage ε(T), asdiscussed above, the relative shrinkage ε_(r)(T) is preferably betweenlimiting values in some specific temperatures.

First, for low temperatures, the relative shrinkage should be reasonablylow. This is because the temperature during transportation may rise suchthat some shrinkage occurs. Thus, even if the film, when applied on abody, has already shrunk to some extent, the shrinkage potential of thefilm is still high, since the relative shrinkage is low.

Second, for high temperatures, the relative shrinkage should bereasonably high. This is because films that are purposely heat treatedhave preferably used most of their shrinkage potential. For example,when the crushed film floats on water, e.g. hot water, the crushedpieces are preferably not further shrunk on the water. For example, thecrushed pieces may be collected using a sieve having a size, and furthershrinking of the pieces might make the smaller than the sieve size. Thustheir collection might become hard. Furthermore, the further shrinking,as discussed, might curve or bend the crushed pieces, and the furtherutilization of such curved pieces might be more problematic than theutilization of planar pieces. The heat shrunk label would not have toomuch residual shrinkage potential left. High shrinkage potential of thelabel may be harmful when heated liquid (having a temperature around 80°C.) is used during the separation process, which will cause e.g. curlingof the label into tight tubes blocking the washing apparatus.

According to an embodiment, a heat shrinkable (thermally shrinkable)label film having a first length L₀ in a first direction before heattreatment and a second length L(T) in the first direction after heattreatment wherein the temperature of the thermally shrinkable label filmhas been T, whereby

-   -   the thermally shrinkable label film has a temperature dependent        shrinkage ε(T)=[L(T)−L₀]/L₀, wherein    -   the shrinkage of the thermally shrinkable label film, after a        thermal treatment such that the temperature of the thermally        shrinkable label film has been T=98° C., is ε(98° C.), wherein    -   the value of ε(98° C.) is less than −0.45, optionally at most        −0.85;    -   the shrinkage of the thermally shrinkable label film, after a        thermal treatment such that the temperature of the thermally        shrinkable label film has been T=65° C., is ε(65° C.), wherein    -   the value of ε(65° C.) is greater than −0.10, preferably greater        than −0.07; optionally at most 0;        and    -   the thermally shrinkable label film has a relative temperature        dependent shrinkage ε_(r)(T)={[L(T)−L₀]/L₀}/ε(98° C.), wherein    -   the difference between the values of the relative temperature        dependent shrinkage ε_(r)(T) for at least one pair of        temperatures T₂ and T₁ having a difference T₂−T₁=15° C., i.e.        ε_(r)(T₂)−ε_(r)(T₁), is more than 50 percentage points; wherein        the lower of the two temperatures of the pair, T₁, is from        65° C. to 70° C.

In the previously presented, the lower of the two temperatures T₁ may be65° C. The difference between the values of the relative temperaturedependent shrinkage ε_(r)(T) for at least the pair of temperaturesT₂=85° C. and T₁=65° C., i.e. ε_(r)(T₂)−ε_(r)(T₁), may be more than 65percentage points, preferably more than 70 percentage points.

According to another embodiment, a heat shrinkable (thermallyshrinkable) label film having a first length L₀ in a first directionbefore heat treatment and a second length in the first direction L(T)after heat treatment wherein the temperature of the thermally shrinkableplastic film has been T, whereby

-   -   the thermally shrinkable label film has a temperature dependent        shrinkage ε(T)=[L(T)−L₀]/L₀, wherein    -   the value of the temperature dependent shrinkage ε(T) for the        temperature T=65° C. is greater than −0.10, and    -   the value of the temperature dependent shrinkage ε(T) for the        temperature T=80° C. is less than −0.25.

According to another embodiment, a heat shrinkable (thermallyshrinkable) label film having a first length L₀ in a first directionbefore heat treatment and a second length L(T) in the first directionafter heat treatment wherein the temperature of the thermally shrinkablelabel film has been T, whereby

-   -   the thermally shrinkable label film has a temperature dependent        shrinkage ε(T)=[L(T)−L₀]/L₀, wherein    -   the shrinkage of the thermally shrinkable label film, after a        thermal treatment wherein the temperature of the thermally        shrinkable label film has been T=98° C., is ε(98° C.), wherein    -   the value of ε(98° C.) is less than −0.45, optionally at most        −0.85; and    -   the thermally shrinkable label film has a relative temperature        dependent shrinkage ε_(r)(T)={[L(T)−L₀]/L₀}/ε(98° C.), wherein    -   the value of the relative temperature dependent shrinkage        ε_(r)(T) for the temperature T=65° C. is less than 10% and    -   the value of the temperature dependent shrinkage ε_(r)(T) for        the temperature T=80° C. is more than 45%.

A large shrinkage potential may be obtained, for example, by polymercompounds such as cyclic olefin copolymers, where the seaming may beperformed using other methods, such as laser welding or heat-sealing ofouter layers. Laser welding or heat-sealing of outer layers in generalmay be used to provide seam which withstands large shrinkage of thelabel without opening of the seam. However, this may not be practical toimplement in every application. In general, a multilayer film comprisinglarge shrinkage potential refers to a multilayer film preferred inlabelling methods, where the shrink label is placed around the surfaceof the items to be labelled as a sleeve or a seamed tube, which may thenbe shrunk against the item to be labelled without an adhesive to holdthe label in place.

In some embodiments, a multilayer film may be configured to shrink lessin a given temperature range. In general, a multilayer film comprisingless shrinkage potential refers to a multilayer film preferred inlabelling methods, where the shrink label is roll-fed on the surface ofthe item to be labelled and seamed from at least one end of the labelagainst the item to be labelled by an adhesive. This may be preferred,for example, to obtain a sufficiently large shrinkage for the label toattach tightly against a container surface, but at the same time toprevent the opening of the seam. In particular, a seam comprising anultra-violet (UV) radiation curable hot melt adhesive may not stand verylarge tension forces due to shrinkage, and may consequently break whentoo large shrinkage occurs. Therefore, for at least some hot meltadhesive based seaming methods, it may be preferred that the multilayerfilm comprises less shrinkage potential. This may be obtained, forexample, by using polymer compounds such as copolymers or terpolymers ofpropylene.

Therefore, according to an embodiment, a heat shrinkable (thermallyshrinkable) label film having a first length L₀ in a first directionbefore heat treatment and a second length L(T) in the first directionafter heat treatment wherein the temperature of the thermally shrinkablelabel film has been T, whereby

-   -   the thermally shrinkable label film has a temperature dependent        shrinkage ε(T)=[L(T)−L₀]/L₀, wherein    -   the shrinkage of the thermally shrinkable label film, after a        thermal treatment such that the temperature of the thermally        shrinkable label film has been T=98° C., is ε(98° C.), wherein    -   the value of ε(98° C.) is less than −0.30, optionally at most        −0.60;    -   the shrinkage of the thermally shrinkable label film, after a        thermal treatment such that the temperature of the thermally        shrinkable label film has been T=65° C., is ε(65° C.), wherein    -   the value of ε(65° C.) is greater than −0.10, preferably greater        than −0.07; optionally at most 0;        and    -   the thermally shrinkable label film has a relative temperature        dependent shrinkage ε_(r)(T)={[L(T)−L₀]/L₀}/ε(98° C.), wherein    -   the difference between the values of the relative temperature        dependent shrinkage ε_(r)(T) for at least one pair of        temperatures T₂ and T₁ having a difference T₂−T₁=15° C., i.e.        ε_(r)(T₂)−ε_(r)(T₁), is more than 50 percentage points; wherein        the lower of the two temperatures of the pair, T₁, is from        65° C. to 70° C.

In the previously presented, the lower of the two temperatures T₁ may be65° C. The difference between the values of the relative temperaturedependent shrinkage ε_(r)(T) for at least the pair of temperaturesT₂=85° C. and T₁=65° C., i.e. ε_(r)(T₂)−ε_(r)(T₁), may be more than 65percentage points, preferably more than 70 percentage points.

According to another embodiment, a heat shrinkable (thermallyshrinkable) label film having a first length L₀ in a first directionbefore heat treatment and a second length in the first direction L(T)after heat treatment wherein the temperature of the thermally shrinkableplastic film has been T, whereby

-   -   the thermally shrinkable label film has a temperature dependent        shrinkage ε(T)=[L(T)−L₀]/L₀, wherein    -   the value of the temperature dependent shrinkage ε(T) for the        temperature T=65° C. is greater than −0.10, and    -   the value of the temperature dependent shrinkage ε(T) for the        temperature T=80° C. is less than −0.15.

According to another embodiment, a heat shrinkable (thermallyshrinkable) label film having a first length L₀ in a first directionbefore heat treatment and a second length L(T) in the first directionafter heat treatment wherein the temperature of the thermally shrinkablelabel film has been T, whereby

-   -   the thermally shrinkable label film has a temperature dependent        shrinkage ε(T)=[L(T)−L₀]/L₀, wherein    -   the shrinkage of the thermally shrinkable label film, after a        thermal treatment wherein the temperature of the thermally        shrinkable label film has been T=98° C., is ε(98° C.), wherein    -   the value of ε(98° C.) is less than −0.30, optionally at most        −0.6; and    -   the thermally shrinkable label film has a relative temperature        dependent shrinkage ε_(r)(T)={[L(T)−L₀]/L₀}/ε(98° C.), wherein    -   the value of the relative temperature dependent shrinkage        ε_(r)(T) for the temperature T=65° C. is less than 10% and    -   the value of the temperature dependent shrinkage ε_(r)(T) for        the temperature T=80° C. is more than 45%.

In above, the ε(T) referred to the shrinkage of a film, and ε_(r) (T) tothe relative shrinkage of a film, defined as ε(T)/ε(98° C.). Theshrinkage may as well be expressed as a percentage difference of thelength of a non-shrinked multilayer film in relation to a shrinkedmultilayer film, as described hereafter. Therefore, according to anembodiment, the shrinkage of a multilayer film at temperatures between80 and 150° C., preferably between 80 and 110° C., more preferablybetween 80 and 90° C. may be expressed to be more than 20% in theorientation direction of the multilayer film. Preferably, shrinkage maybe in the range of 20 to 40%, or in the range of 40 to 60%, or more than60%, for example at least 70% in the direction of the orientation of themultilayer film. Referring to FIG. 4, the orientation direction may beparallel to S_(x). The shrinkage may be in the range of 20 to 90%,preferably in the range of 25 to 80%, and most preferably in the rangeof 30 to 75% under conventional shrink film and label shrinkingtemperatures in the range of 80 to 150° C., preferably in the range of80 to 130° C., more preferably in the range of 80 to 110° C., morepreferably in the range of 80 to 90° C. in a steam-tunnel. In other thanorientation direction, the multilayer film may have shrinkage less than10%, preferably less than 7%, most preferably less than 5%, for examplein the range of 0 to 5% or in the range of 2 to 4%. Referring to FIG. 4,the other than orientation direction may be direction parallel to S_(y).The shrink performance of the multilayer film is adequate in order toconform the film to the profile of the substrate, which is to belabelled.

Furthermore, according to an embodiment, the shrinkage of the multilayerfilm in the direction of the orientation of the multilayer film may bein the range of 20 to 75% at a temperature range between 65 and 85° C.Preferably, the multilayer film and a label comprising the multilayerfilm is able to shrink in the range of 25 to 65% at a temperature rangebetween 65 and 85° C. For example, the multilayer film and a labelcomprising the multilayer film is able to shrink in the range of 25 to55%, or preferably in the range of 30 to 40% at a temperature rangebetween 65 and 85° C. According to another example, the multilayer filmand a label comprising the multilayer film is able to shrink in therange of 35 to 65%, or preferably in the range of 40 to 60% at atemperature range between 65 and 85° C. At temperature below 65° C. themultilayer film and the label comprising the multilayer film shrinkagemay be less than 10%, preferably less than 5%, for example in the rangeof 0 to 10%, or in the range of 0.5 to 5%. The specific shrinkageprofile of the multilayer film and the label comprising the multilayerfilm has an effect of on providing more controlled shrinkage behaviourfor the film at a specific temperature. For example, specific shrinkingcurves of some/all embodiments may have an effect on more accurateshrinkage to be achieved even if some variation occurs during thermaltreatment (shrinking process).

The composition of the multilayer film according to at least someembodiments has an effect on providing adequate shrinkage level for thelabel, preferably at least 65% shrinkage at 85° C., which is furtheradvantageous during washing in subsequent recycling process. The heatshrunk label would not have too much residual shrinkage potential left.High shrinkage potential of the label may be harmful when heated liquid(having a temperature around 80° C.) is used during the separationprocess, which will cause e.g. curling of the label into tight tubesblocking the washing apparatus.

In some embodiments, as said above, a multilayer film may be configuredto shrink less in a given temperature range. Depending of the type of aheat shrink film and heat shrink label seaming method, the heatshrinkable film or label may comprise a different potential forthermally inducible shrinkage. When expressed as a percentage differenceof the length of a non-shrinked multilayer film in relation to ashrinked multilayer film, a multilayer film may comprise a compositionenabling a large stretching in a monoaxial direction and a seamwithstanding large tension forces, the thermally inducible shrinkage maybe at least 15% preferably at least 25% or at least 35% shrinkage in thetemperature range of 65 to 80° C. or as described above. In particular,large thermally inducible shrinkage may be obtained on multilayer filmsstretched in transversal direction and cut to shrink sleeves, which areseamed and cut to a tubular label prior to labelling. For a multilayerfilm stretched in a monoaxial direction and used as a roll-fed shrinklabel or where ultra violet radiation curable hot melt adhesives areused, the thermally inducible shrinkage may be on a different range. Inparticular, when ultra-violet (UV) radiation curable and/or hot meltadhesive is used for seaming the label to an item, such as when usingmultilayer film or label oriented in machine direction, the heatshrinkable film or label may comprise equal to or less than 60%,preferably equal to or less than 55%, most preferably equal to or lessthan 50% shrinkage in a temperature of 98° C. At a temperature of 98°C., the shrinkage may be equal to or more than 30%, preferably equal toor more than 35%, most preferably equal to or more than 40%. Forexample, at a temperature of 98° C., the shrinkage may be in the rangeof 30% to 60%, preferably in the range of 35% to 55%, most preferably inthe range of 40% to 50%. At a temperature range between 65 and 85° C.,the heat shrinkable film or label may comprise equal to or less than55%, preferably less than 50%, most preferably, less than 45% shrinkage.At a temperature range between 65 and 85° C., the shrinkage may be equalto or more than 20%, preferably equal to or more than 25%, mostpreferably equal to or more than 30%. For example, at a temperaturerange between 65 and 85° C., the shrinkage may be in the range of 20% to55%, preferably in the range of 25% to 50%, most preferably in the rangeof 30% to 45%. In other than orientation direction, the films may haveshrinkage less than 10%, preferably less than 7%, most preferably lessthan 5%, for example between 0 and 5% or between 2 and 4%, expressed asa percentage difference of the length of a non-shrinked multilayer filmin relation to a shrinked multilayer film. Referring to FIG. 4, theother than orientation direction may be direction parallel to S_(y). Theshrink performance of the multilayer films is adequate in order toconform the film to the profile of the substrate, which is to belabelled. Multilayer film(s) which are not able to shrink as presentedabove are not suitable for face films of labels and are thus notsuitable for heat shrink labelling applications. A heat shrinkable labelcomprises or consists of a face film configured to shrink between 15 and70%, at a temperature range between 65 and 85° C. In addition, the heatshrinkable label comprises or consists of a face film configured toshrink less than 10% at temperature below 65° C.

Therefore, a multilayer film may be configured to shrink in thedirection of the orientation of the multilayer film at least 15%,preferably at least 25%, or preferably at least 35% at a temperaturerange between 65 and 85° C. Furthermore, the multilayer film may beconfigured to shrink less than 10% at a temperature below 65° C. Themultilayer film may be configured to shrink in the direction of theorientation of the multilayer film, for example, in the range of 20 to75% or in the range of 25 to 65% at a temperature range between 65 and85° C. Alternatively, when less shrinkage is preferred, the multilayerfilm may be configured to shrink in the direction of the orientation ofthe multilayer film equal to or less than 60%, preferably equal to orless than 55%, most preferably equal to or less than 50%, at atemperature of 98° C. For example the multilayer film may be configuredto shrink in the direction of the orientation of the multilayer filmequal to or more than 20%, preferably equal to or more than 35%, mostpreferably equal to or more than 40%, at a temperature of 98° C. Themultilayer film may be configured to shrink in the direction of theorientation of the multilayer film, for example, in the range of 30 to60%, preferably in the range of 35 to 55%, most preferably in the rangeof 40 to 50%, at a temperature of 98° C. The multilayer film may beconfigured to shrink in the direction of the orientation of themultilayer film equal to or less than 55%, preferably equal to or lessthan 50%, most preferably equal to or less than 45%, at a temperaturerange between 65 and 85° C. The multilayer film may be configured toshrink in the direction of the orientation of the multilayer film equalto or more than 20%, preferably equal to or more than 25%, mostpreferably equal to or more than 30%, at a temperature range between 65and 85° C. The multilayer film may be configured to shrink in thedirection of the orientation of the multilayer film, for example, in therange of 20 to 55%, preferably in the range of 25 to 50%, mostpreferably in the range of 30 to 45%, at a temperature range between 65and 85° C. By shrinkage in the direction of the orientation of themultilayer film it is meant, that the multilayer film shrinksessentially towards the state prior to orientation, as shown for examplein FIG. 5 by directions DIR1 and DIR1′.

The multilayer film according to at least some/all embodiments maycomprise a shrink force in the orientation direction of the face filmduring heating at temperatures between 60 and 98° C. of less than 10N/15mm, or less than 8N/15 mm, or in the range of 1 to 10N/15 mm, or in therange of 2 to 8 N/15 mm. Adequate shrink force is needed for the properfitting of the label around an item when heat is applied.

FIG. 4 illustrates an embodiment of a label having a thermally inducibleshrinkage potential. The label 900 may be obtained from a monoaxiallystretched multilayer film 100, for example by cutting. The label 900comprises a first surface 901 and a second surface 901, which may besurface treated to improve the printability of the label 900. The label900 comprises a primary length h1, a primary width w1 and a primarythickness d1 dimensions in a first temperature T₁. The temperature T₁refers to the lower of the pair of two temperatures T₂ and T₁, which maybe used to define a relative temperature dependent shrinkage ε_(r)(T).Each multilayer film 100 may comprise an initial shrinkage temperatureT_(shr), below which there exists only residual thermally inducibleshrinkage, such as less than 10%. The initial shrinkage temperatureT_(shr) may be a temperature equal to or more than 60° C., preferablyequal to or more than 65° C. For processability, the initial shrinkagetemperature T_(shr) in general may be equal to or less than 70° C. Whenproviding heat HEAT1 to a multilayer film 100 comprising a thermallyinducible shrinkage potential, the thermally inducible shrinkage maytake place in a second temperature T₂ equal to or higher than theinitial shrinkage temperature T_(shr). The second temperature T₂ may be,for example, in the range of 65° C. to 90° C., preferably in the rangeof 65° C. to 85° C. The thermally inducible shrinkage may be arranged toreduce a dimension of the multilayer film 100 in a first direction DIR1between the first temperature T₁ and the second temperature T₂ having atemperature difference of 15° C. in the range of 15% to 50%, preferablyin the range of 15% to 40%. Therefore, after thermally inducedshrinkage, the label 900 may comprise a secondary length h2, a secondarywidth w2 and a secondary thickness d2. The difference between thesecondary length h2 and the primary length h1 refers to the extent ofthermally inducible shrinkage potential. Depending of the shape of theitem to be labeled, the stretching direction DIR1 and the multilayerfilm 100 composition, the width w2 dimension of the label 900 indirection DIR2 may change. When the cross-sectional profile of the itemin direction DIR2 remains essentially constant, the width w2 dimensionof the label 900 in direction DIR2 may remain essentially the same.However, when the cross-sectional profile of the item in direction DIR2changes along direction DIR2, the width w2 dimension of the label 900 indirection DIR2 may change accordingly. Preferably, the first temperatureT₁ and the second temperature T₂ may both be in the range of 65° C. to85° C. The degree of thermally inducible shrinkage correlates withtemperature and the stretching ratio, such that a higher temperatureabove the initial shrinkage temperature T_(shr) in general leads toincreased shrinkage. In addition, a higher stretching ratio of amultilayer film in general leads to higher thermally inducible shrinkagepotential.

FIG. 5 shows an example embodiment of a thermally induced shrinkage fora label. A label 900 comprising thermally inducible shrinkage potentialmay be obtained from a multilayer film stretched in a first directionDIR1. The label 900 may be wrapped around an item to form a seam 990comprising overlapping areas of the first surface 901 and the secondsurface 902. The overlapping areas of the tubular film may be seamed bya suitable means, such as laser welding or using an adhesive. When thefirst direction DIR1 of stretching of a thermally inducible shrinkablemultilayer film is in a transversal direction, a length of themultilayer film in a second direction DIR2 may first be cut and wrappedaround a cylindrical body, such as a mandrel, for seaming said length ofmultilayer film prior to cutting a shrink sleeve label. In particular,on transversally stretched shrink sleeves, an adhesive solvent may beused to attach overlapping surfaces of a multilayer film to form theseam. An adhesive solvent is a solvent, which melts the overlappingouter surfaces 901, 902 of the film sufficiently for the surfaces 901,902 to attach against each other. As an alternative for a solvent, a UVcurable hot melt adhesive may be used for the seaming. By providing heatHEAT5 to a seamed label 900 cut from the multilayer film, for example ina shrink tunnel, such that the label is heated to a temperature equal toor higher than the initial shrinkage temperature T_(shr), the label 900may be shrinked, The principal direction of shrinkage DIR1′ is adirection parallel to the first direction DIR1 of stretching. Whendisposed around the outer surface of the item, the shrinkage of theround sleeve may follow the contours of the item surface such that ashrink tension is formed to hold the sleeve in place against the labeleditem.

The stretching may be performed in a single direction DIR1 of the film,such as in machine direction, which refers to the longitudinal directionof the film in the production process. Films stretched in machinedirection may be referred to as machine direction oriented (MDO) films.In MDO films the polymer chains are oriented monoaxially in the machinedirection. Machine direction oriented films may be used for roll-fedlabelling, i.e. in a labelling process where the film may be suppliedfrom a reel, printed, cut into sheets referred to as labels and mountedaround an item and seamed during the labelling step. The seaming may bedone by various means, such as by using an adhesive, or a laser weldingmethod, for example. The adhesives may be, for example, hot-meltadhesives or ultra-violet curable hot-melt adhesives.

In general, the flow rate properties of the polymer compounds and/orblends used on a multilayer film 100 may determine the stretchingcapability and quality of the multilayer film 100 to a significantextent. In particular, the melt flow rate (MFR) of each polymer ispreferably matched to similar levels, to obtain even flow of the moltenmass on an extruder. The melt flow rate is a measure of the ease of flowof melted plastic, such as a polymer compound in a melted state. Meltflow rate is inversely proportional to shear viscosity. The melt flowrate of plastics may be determined according to a ISO 1133:2005standard. In addition to the melt flow rate, glass transitiontemperature may be used to characterize the processability of polymercompounds in the manufacturing of a multilayer film 100. In temperaturesabove the glass transition temperature, polymer chains may slide pasteach other more easily when a force is applied. As a rule of thumb, theglass transition temperature of the polymer compound defines to a largeextent the lower temperature, where a multilayer film 100 consisting ofthe polymer compound may be stretched. In a similar manner, a blend ofcompounds may be stretched in a temperature equal to or higher than theglass transition temperature of any of the polymer compounds in themultilayer film 100. Preferably, the multilayer film 100 may bestretched in a temperature equal to or higher than at least 10° C. abovethe glass transition temperature of the polymer compound(s) and/orblend(s) in the multilayer film 100. When using polymer compounds orblends having a higher glass transition temperature, the extent ofstretching may be increased. However, a polymer compound having anincreased glass transition temperature may also have an increasedinitial shrinkage temperature T_(shr). The stretching temperature range,in general, may be in the same temperature range as the thermallyinducible shrinkage, as during thermally induced shrinkage a multilayerfilm in an oriented state principally reverts towards the non-oriented(initial) state before stretching.

Heat shrinkable films may be used for labels on many applications. Whilea label film (face film) may have a monolayer structure, a heat shrinklabel preferably comprises a multilayer structure comprising heat shrinkplastic film layer(s). In addition, the shrink label in generalcomprises at least some graphics on a surface of the face film. Inaddition, the shrinkable label may comprise an adhesive. The adhesivemay be applied only in a joint area of cylindrical label, wherein theopposite edges of the face film are overlapping. For example, theadhesive may be applied between the overlapping edges. Alternatively orin addition, the adhesive may be applied between the face film andsurface of an item to be labelled. Shrinkage of label may be focused ona local area or to the whole label area. Local shrinkage may be focusedon required areas, for example on an edge area of a label. Whole labelmay be shrinked in a direction extending circumferentially around acontainer to conform to the outside (external) shape of the container.Local shrinkage may be focused on required areas, for example on an edgearea of an article.

FIG. 6 shows an example embodiment of labelling an item 400 with a label900 comprising thermally inducible shrinkage. An item 400 may comprisean outer surface 401. The item 400 may be, for example a container, suchas a bottle, jar, canister or a can and may comprise a sealable opening450. The sealable opening 450 may be used as an inlet for introductionof material, such as beverage, food, cosmetics, detergents, or otherconsumables. The sealable opening 450 may comprise a seal, such as a capor a cork or a stopper to prevent the material from coming out from theinterior of the item 400 during transportation or storage. The materialmay have been introduced into the item 400 before providing a label 900on the item 400. The label 900 may comprise a thermally inducibleshrinkage. The label may be obtained from a multilayer film, andcomprises a length, width and thickness. The label may be comprise afirst surface 901 and the second surface 902. The first surface 901 andthe second surface 902 may be adjoined or seamed such that a firstsurface portion of the first surface 901 and a second surface portion ofthe second surface 902 may be adjoined to each other. A seamed label mayform a hollow tube referred to as a sleeve. The first surface 901 may bereferred to as the inner surface facing the item 400 and the secondsurface 902 may be referred to as the outer surface. The overlappingportions of the tubular label 900 may be seamed by any suitable means,such as laser welding, using a solvent or by using an adhesive.Furthermore, the first surface 901 of the label 900 may be attached tothe surface 401 of the item 400 by an adhesive, such as a hot meltadhesive, at least from the area covering the seamed portion of thesleeve. The first surface 901 and/or the second surface 902 of the label900 may comprise printed graphics 920. Preferably, the label 900 maycomprise at least some printed graphics 920 on the first surface 901and/or the second surface 902. The printed graphics 920 may comprise,for example, printed information 910 and/or decoration. The graphics maycomprise, for example one or more colours. The labels may be printed byusing printing inks. In printing on shrinkable labels with flexographicor other types of printing inks, the printing conditions, such astemperatures and chemical compatibility of the layer and the printingink should be considered. For example, lack of solvent evaporation maycause printing ink drying related problems, while an increase in thesolvent or curing temperature may cause a premature shrinkage on themultilayer film. Suitable printing ink for labels may comprise, forexample a ultraviolet radiation (UV) curable printing ink or awater-based or a solvent-based printing ink. In particular, labelsurface material which does not require a surface treatment forprinting, ultraviolet radiation (UV) curable printing ink may besuitable. When a label surface material does not require a surfacetreatment for printing, a solvent-based printing ink may be suitable.The label may be stretched in a first direction DIR1. The direction DIR1of the stretching may be parallel to a multilayer film orientationdirection, such as the multilayer film machine direction or themultilayer film transverse direction perpendicular to machine direction.When forming a seamed sleeve, the stretching in the first direction DIR1may be a surface direction perpendicular to a second direction DIR2,wherein the second direction DIR2 is in general parallel or essentiallyparallel to the longitudinal axis AX1 of the item 400, as shown in FIG.6. The longitudinal axis AX1 may further be defined as the directionessentially perpendicular to the surface normal N_(surf) of the label900, when a seamed tubular label is dropped on place around the item400. A label 900 stretched above the glass transition temperature maycomprise thermally inducible shrinkage potential. The label may bearranged to shrink by providing external energy HEAT4 to the label 900.A thermally shrinkable label may shrink when exposed to an elevatedtemperature. In general, the stretching in a first direction DIR1 andthe thermally inducible shrinkage may be performed on a similartemperature range, as during thermally induced shrinkage a multilayerfilm in an oriented state principally reverts towards the non-oriented(initial) state before stretching. The external energy HEAT4 may beapplied by various means, such as by long wavelength radiation, steam,hot air or by any combination of these. Long wavelength radiation maybe, for example, infra-red range radiation. In response to theapplication of external energy, the thermally inducible shrinkable labelmay be arranged to shrink. Due to shrinkage, the second surface 902 ofthe label 900 is pressed against the exterior surface 901 of the item900. Due to the tension force, a shrinkable label 900 may be arranged toprovide a strengthening force for the item 900, such as a recyclableplastic container. As the printing of graphics 920 in general isperformed prior to labelling an item 400, the shape and size of theprinted graphics 920 may change significantly due to the shrinkage ofthe heat shrink label 900, as shown in FIG. 6. In particular, a suitableprinting ink and printing method for thermally shrinkable multilayerfilms may be selected such that the shrinkage properties of the printedgraphics 920 consisting of printing ink(s) after thermally inducedshrinkage are of good quality. For example, the adhesion, re-wetting andshrinkage properties have an effect on the appearance of the printedgraphics 920 on a label 900 surface.

The labelling may be used to obtain a labelled item 1004. A labelleditem 1004 refers to a combination of a heat shrink label 900 and an item400. The label 900 may comprise a continuous multilayer film around theexternal or outer surface 901 of the item 400. The continuous multilayerfilm may be oriented in one direction DIR1 and may comprise a core layerand a first and a second skin layers. In particular, a multilayer filmmay comprise mechanical, optical and thermodynamic properties, whichimprove the use of such a film for labels. The combination of a heatshrink label 900 and an item 400 may comprise items having outer surface401 curvature or an uneven surface. A difference between the smallestdiameter and the largest diameter of an item may be, for example between20 and 80%. Preferably, the item 400 may comprise less surface 401curvature, such as between 30 and 70%, for example. The manufacturingmethods for many plastics allow means for providing outer surfaces 401comprising curvature or other irregular shapes. For example, mouldingmethods may be used to provide plastic items having a variety of shapes.In consumer bottles, the use of polyethylene terephthalate is common.The combination of a heat shrink label 900 and an item 400 is preferredespecially in applications wherein the item is a bottle consisting ofpolyethylene terephthalate.

Labels are increasingly used as carriers of information on variousitems, such as on the surfaces of moulded products or containers. Thelabels may be provided with means to tightly contact the surface of thelabel with the surface of the item, and follow the contours of the itemsurface. Examples of items where labels obtained from multilayer filmsmay be used are products or containers having various shapes, such as,jars, bottles, trays, boxes, grocery containers and dairy productcontainers. Furthermore, shrinkable labels may be used for containerssuch as plastic bottles and glass jars for consumer drinks or food. Theheat shrink labels may further be used for label laminates comprising anadhesive layer for attaching the label to an item. However, inparticular, heat-shrink sleeves or labels may be used on recyclableplastic containers, such as PET bottles, where the recyclability of thematerial is pending on the ability to separate the labels from thelabelled items. Materials having a density less than or more than 1.00g/cm³ may be used for separation with water. In particular, a multilayerfilm comprising a density less than 1.00 grams per cubic centimeter(g/cm3) may be a preferred material for thermally inducible shrinkablelabels, due to floatability in water. After crushing bulky objects tosmall pieces for removing any air pockets, materials comprising adensity of less than 1.00 g/cm³ will remain on the surface of the water,whereas materials comprising a density of more than 1.00 g/cm³ will sinkdue to specific gravity. Therefore, preferably polymer materialscomprising a density of less than 1.00 g/cm³, such as between 0.90 and0.98 g/cm³ may be used to obtain a multilayer film having a density lessthan 1.00 g/cm³, preferably between 0.90 and 0.98 g/cm³, most preferablybetween 0.90 and 0.95 g/cm³.

Film Properties and Printability

When selecting the polymer compounds for the core and the skin layers, abalance between the end use requirements and the manufacturingconditions should be considered. For example, in the end use, and in theskin layers in particular, the heat resistance of the multilayer filmsurface should be at least sufficiently maintained for applicationsrequiring high temperatures in the range of 80° C. to 100° C., such aswith containers filled with hot substances, such as food or beverages.Blocking refers to a permanent attachment of an multilayer film outersurface to another surface, such that the multilayer film may not beseparated again. Blocking may occur, for example, during multilayer filmstorage. Elevated temperatures and/or increased pressure may increasethe tendency for blocking, therefore an anti-blocking agent and/or aslip additive may be used for reducing the risk of blocking a woundmultilayer film roll. An amount of anti-blocking agent may be in therange of 0.5 and 5% by weight, preferably in the range of 1 and 3% byweight, or between 2 and 3% by weight. Further, skin layer(s) maycontain additives, such as inorganic fillers, pigments, antioxidants,ultraviolet absorbers, antistatic additives or cavitating agents tochange the visual appearance or characteristics of the surface layers.Furthermore, the melting temperature of the polymer compounds maypreferably be less than 125° C., such as less than 120° C., or less than110° C., such as in the range of 60° C. to 120° C. or in the range of80° C. to 120° C.

For printability, the surface tension of a surface should be high. Ahigh surface tension refers to surface having a surface tension equal toor more than 36 mN/m for printability, preferably at least 38 mN/m or atleast 44 dynes/cm measured according to the standard ASTM D-2578. Thesurface tension may be between 36 and 60 dynes/cm, preferably between 38and 56 dynes/cm or between 44 and 50 dynes/cm. A low surface tension maylead to poor retaining capability of printing ink applied to thesurface. To obtain such surface tension levels, a surface treatment maybe performed on at least one skin layer surface prior to printing, suchas a corona, flame or plasma treatment. Furthermore, the surface shouldcomprise sufficient compressibility, for the printing to be absorbedand/or attached on the surface or surface layer of a multilayer film.Some polymer compounds, especially homopolymers, copolymers andterpolymers of propylene, may require a surface treatment, such as acorona, flame or plasma treatment, to increase the level of surfacetension for printability. On the other hand, compounds such as cyclicolefin copolymers in general comprise high surface tension levels and donot require a surface treatment.

High printing quality comprises, for example, excellent ink adhesion andregister control, allowing for example gravure and flexographicprinting. The printing may be multi-layered comprising two or moreprinting layers. For example, colour printing at the film surface may becovered (overprinted) with a white or some other colour printing. Thus,the overprinting may be next to the surface of the item. Through thiskind of label the object beneath is not visible.

Each layer in a multilayer film may be designed to improve thefunctionality of the multilayer film as a label. The labels in generalare designed to be printable, for example by means of flexographicprinting, rotogravure printing, hot-melt printing or digital printing.In particular, technologies using rolls to transfer the images, such asflexographic printing, are suitables method for medium to large seriesof labels. Flexographic printing may comprise the use of various typesof printing inks, such as solvent-based inks, water-based inks, electronbeam curing inks or ultraviolet light (UV) curing inks, to name a few.

The properties of the skin layer may be matched with the printingmethod. The printing method may comprise, for example, the use of awater-based or a solvent-based printing ink, ultra-violet light curableprinting ink or a heat-transfer printing ink. Heat-transfer printinginks in general refer to printing inks which are solid at ambienttemperature and liquid at the time of printing, and do not comprise orform volatile organic compounds (VOCs) during printing.

As an alternative, printing of a multilayer may be performed usingwater-based or solvent-based printing inks. When applied on a surface,the water-based or solvent-based printing ink may either dry or cure. Ingeneral, such printing inks may be dried or cured in lower temperaturesthan may be required for thermal transfer printing inks. In drying, thewater or solvent present in the printing ink may evaporate from thesurface. Furthermore, the water-based or solvent-based inks may comprisespecific components to reduce drying times. Fast drying times are arequirement on processes where large series of graphics need to beprinted on a multilayer film. However, while additives such as waxes,surfactants, oils, or silicone may reduce the drying time, they may alsoreduce the ability of the printing ink to stick to the surface of amultilayer film. In particular, this may be a problem with multilayerfilm surfaces having low surface tension or absorbance properties.Therefore surfaces having low surface tension or absorbance properties,such as a skin surface comprising a homopolymer, copolymer ortermpolymer of propylene for example, may require a surface treatment toimprove the printability.

When cured, a water-based or solvent-based printing ink may undergocross-linking and/or polymerization reactions, which bind the ink to theprinted surface. Printing ink curing may be arranged to take place, forexample by evaporation of a solvent, by oxidation, by polymerizationreactions due to radiation, such as ultra-violet radiation, byprecipitation, or by a combination of these methods, depending of theprinting ink formulation. Selection of the proper solvent(s) plays animportant role in the printing of multilayer films. The choice ofsolvent involves more than one factor, such as evaporation rate,solution viscosity, the effectiveness of a solvent depending on itsability to adequately dissolve one material while leaving othermaterials unaffected A solvent in a printing ink should be compatiblewith the printing and the labelling process, for example not cause anadverse chemical reaction, such as welding of the first and the layers,or swelling of the printed area. In particular, the use of compatiblesolvent in a printing ink plays a role with shrink sleeves oriented intransverse direction, where the multilayer film may be first printed,and then seamed to a tubular form with a solvent, prior to cuttinglabels. An incompatible solvent may, for example cause an excessiveswelling of a solvent on the printable area.

The principal raw materials of a water-based or solvent-based printingink in general comprise a pigment, a binder, additives and a solvent. Apigment may be a solid substance that alters the appearance of an objectby the selective absorption and/or scattering of light. A pigment maycomprise a certain type of colour, for example, black, white orfluorescent colour. A pigment may colour the solvent-based printing inkand provide gloss, abrasiveness or resistance to light or heat or to asolvent, for example. Pigments such as extenders or opacifiers may alsobe used. Extenders are transparent pigments that make the colours ofother pigments appear less intense. Opacifiers are pigments, which makethe paint opaque (non-transparent) such that the surface below the paintcannot be seen. A binder in general refers to a resin that binds theother ingredients of a water-based or solvent-based printing inktogether for a colloid. Furthermore, the binder enables the attachmentof the water-based or solvent-based printing ink to a surface. Inaddition to pigment, a binder may contribute to gloss and resistance toheat, blocking, chemicals and water. A water-based or solvent-basedprinting ink may comprise more than one resin as a binder. A binder maycomprise, for example, one or more of the following general types ofcompounds: acrylics, ketones, epoxides, polyvinylbutyral alkyds,maleics, fumarics, polyamides, cellulose derivatives, such as celluloseesters, formaldehydes, hydrocarbons, rubber resins, phenolics orpolyurethanes. Additives may be used to alter the properties of thesolvent-based printing ink. Additives may be, for example plasticisersto enhance the flexibility of the printed film, wax to promote rubresistance, drier to catalyse an oxidation reaction for inks dryable byoxidation, chelating agent to increase the viscosity of the ink,antioxidant to delay the onset of an oxidation polymerization,surfactant to improve wetting, stabilizing agents for pigmentdispersion, alkali to control the viscosity/solubility of acrylic resinsin water based inks, humectants to retard premature drying or pHmodifiers. Solvents and water are used to keep the printing ink inliquid form from the period when it is applied to the printing plate orcylinder until when it has been transferred to the surface to beprinted. At this point the solvent or water separates from the printingink to allow the printed graphic to dry and bind to the surface. Inparticular, some printing methods, such as gravure and flexographicprinting, may require a solvent that evaporates rapidly. Rapidlyevaporating solvents for flexographic printing comprise, for example,ethyl acetate, isopropanol, n-propyl acetate, cyclohexanone,butoxyethanol and butyrolactone, which comprise a relatively low boilingpoint. The evaporation may be enhanced by curing. In particular, inflexographic printing resins based in the reaction products of apolymerized fatty acids (dimer acids) or diamines or a mixture ofdiamines and a terminating monocarboxylic acid may be used. The solventin flexographic printing inks may further comprise a lower alcohol, suchas ethanol, n-propanol, or isopropanol, which evaporate rapidly afterprinting. Flexographic printing inks may also contain some amounts of alower aliphatic ester, such as ethyl acetate or propyl acetate.

Solvent-based and/or ultraviolet radiation (UV) curable printing inksare widely used for thermally shrinkable multilayer films. Inparticular, a suitable printing ink for thermally shrinkable multilayerfilms may shrink such that the printing after thermally inducedshrinkage is of good quality.

The properties of the chemical compounds in the skin layer determine thesurface energy level of the of the multilayer film. Based on the surfaceenergy level the film may need to be surface treated. A multilayer filmsurface comprising a relatively low surface tension level, such as lessthan 38 mN/m, or less than 36 mN/m, may require a surface treatmentprior to printing. A surface treatment may comprise a corona, flame orplasma treatment. When the skin layer comprises copolymer of propylene,such as a multilayer film skin layer comprising homopolymer or copolymeror terpolymer of prolylene, the dyne level in general may be increasedby corona or flame-treatment for improving printability. In particular,a surface treated skin layer comprising copolymer of propylene accordingto an embodiment of the invention may be used for printing with ultraviolet (UV) curable printing ink. Furthermore, a skin layer comprisingcopolymer of propylene according to an embodiment of the invention maybe used for printing with a solvent-based flexographic printing ink or agravure printing ink without a surface treatment. Further still, amultilayer film surface comprising a relatively high surface tensionlevel, such as at least 36 mN/m, or at least 38 mN/m, such as amultilayer film skin layer comprising cyclic olefin copolymer, may notrequire a surface treatment prior to printing. A skin layer comprisingcyclic olefin copolymer according to an embodiment of the invention maybe used for printing with a ultra violet (UV) curable printing ink, asolvent-based flexographic printing ink or a gravure printing ink,without a surface treatment. In general, multilayer films according toat least some embodiments of the invention may be printed successfullywith solvent-based flexographic printing ink or gravure printing ink,wherein the solvent(s) may be dried by evaporation. Solvent-basedflexographic printing ink or gravure printing ink are typically notcured by using ultra violet light. Alternatively, ultra violet (UV)curable offset printing ink or ultra violet (UV) curable flexographicink may also be used for the printing of heat-shrinkable multilayer filmsurfaces. When such multilayer film surface comprises homo- or copolymerof propylene, however, the multilayer film surface may need to bespecially pre-treated, for example top-coated In particular,flexographic and/or rotogravure printing using printing inks comprisingevaporating solvent(s) may be used with shrink label printing, when theprinting ink drying by evaporation of the solvent is performed in atemperature below the initial shrinkage temperature T_(shr) of themultilayer film. Drying of the printing ink at such temperatures mayreduce the thermally induced stress to the multilayer films comprisingthermally inducible shrinkage potential.

Furthermore, the dimensional stability and uniform thickness profile ofthe multilayer film prior to printing is desired. In addition to inkabsorbance, dimensional stability may enhance the print register, whenmultiple printing inks are used to print coloured graphics or text.Between each printing ink, the film may be cured to dry the printing inkbefore next printing step. In addition, the multilayer film may bethermally shrinkable, which further requires that the printing on alabel should be designed to match the end shape of the labelled itemsurface. this also requires a tendency for the multilayer film to bedeformed non-permanently, or elastically. Therefore, modulus ofelasticity and tensile strength may be important characteristics for themultilayer film. In particular, the stiffness, hardness and elasticproperties of the compounds used on the core and skin layers of amultilayer film may control the shrinkage level and behaviour in amultilayer film comprising thermally inducible shrinkage. However, whendispensing a label, stiffness in at least one direction DIR1 isrequired. The direction DIR1 may be parallel in multilayer film machinedirection, or perpendicular to multilayer film machine direction. Ingeneral, higher stiffness may be desirable in the direction of thestretching.

Optical properties of a multilayer film may play a role in the selectionof compatible polymers and additives. In general, haze is a propertyused to describe transparency of a plastic film or a label consisting ofthe plastic film. Haze relates to scattering of light by a film thatresults in a cloudy appearance of the film. Haze corresponds to thepercentage of light transmitted through a film that is deflected fromthe direction of the incoming light. Haze may be measured according tostandard ASTM D1003. The printing of a multilayer film may be performedon a first or a second surface of the multilayer film. In particular, ona shrink sleeve or a heat shrink label, the printing may be on the skinlayer adjacent to a labelled container, such that the skin layers andthe core layer protect the printing, for example from scratching orwearing. Furthermore, in some embodiments only a fraction of the labelmay comprise printing. The container may further be transparent, and theend use may require a “clear-on-clear” effect, wherein the transparencyor the haze is matched between the label and the labelled item.According to an embodiment, the multilayer plastic film is clear i.e.transparent to visible light. Clear multilayer shrink films and labelscomprising said films have good visual appearance. For example, saidfilms may provide no-label look or appearance, when attached to thesurface of an item. The clear no-label look allows the objects beneathsuch label, i.e. the bottle or contents, to be visible through suchlabel. Clarity of the film and a label comprising said film can bemeasured and evaluated by the haze values. The overall haze of themultilayer film and label consisting of said multilayer film may be lessthan 25%, preferably less than 15%, and most preferably less than 10%when measured according to the standard ASTM D1003. For example, thehaze of the face film may be between 2 and 10%, or between 5 and 10%.

From manufacturing point of view, lower processing temperatures for themultilayer film formation by extrusion or casting may be desirable,therefore polymer compounds comprising low glass transition temperaturesmay be preferred. The glass transition temperatures may correlate withthe mechanical properties of the multilayer film.

Definition of Chemical Compounds

Copolymers of Alpha-Olefin and Alkyl Acrylate

Copolymers of alpha-olefin and alkyl acrylate have in general been usedas in the tie layer of a polymer film, in concentrations ranging between1 to 2% by weight. However, it has now been surprisingly been found outthat at least certain acrylate copolymers may in addition be suitablefor core layer polymers of thermally inducible multilayer films. Thecore layer of a multilayer film may thus comprise a copolymer ofalpha-olefin and alkyl acrylate. For example, to create polymers with adifferent set of properties, ethylene may be copolymerized with at leastone comonomer, wherein the comonomer is an alkyl acrylate ester. Theethylene may comprise a low density polyethylene (LDPE), referring to apolyethylene having a density in the range of 0.910 to 0.940 g/cm³.Examples of preferred alkyl acrylate esters suitable for use ascomonomers comprise acrylic acid esters C1 to C8 linear or branchedalcohols. For example, methyl acrylate, ethyl acrylate, n-butylacrylate, iso-butyl acrylate, t-butyl acrylate, n-hexyl acrylate,2-ethylbutyl acrylate, and 2-ethylhexyl acrylate may be used ascomonomers. A particularly preferred comonomer is butyl acrylate, suchas n-butyl acrylate. A copolymer of ethylene and butyl acrylates mayprovide good optical properties in addition to increased softness to themultilayer film, which may be used to improve the stretching propertiesof the multilayer film. Furthermore, the copolymer of ethylene and butylacrylate may increase the heat resistance, such as a higher peak meltingtemperature, in comparison to other polymer compositions generally usedin the core layer of a multilayer film, especially a thermally induciblemultilayer film. Further still, multilayer film properties such as chainmobility and low temperature toughness, may be improved by increasingthe butyl acrylate monomer content of the copolymer. The copolymer ofethylene and butyl acrylate may be a block or random copolymer. Apreferred copolymer of ethylene and butyl acrylate may comprise in therange of 5% to 30% by weight, preferably in the range of 5 to 25% byweight, most preferably in the range of 5 to 15% or in the range of 10to 15% by weight of butyl acrylate monomers. For example, the copolymerof ethylene and butyl acrylate may comprise a n-butyl acrylate contentin the range of 5% to 30% by weight. A copolymer of ethylene and butylacrylate may be particularly suitable as a compound in the core layer tocontrol the free shrinkage behaviour of the film. A copolymer ofethylene and butyl acrylate may further comprise a melting temperaturein the range of 96° C. to 104° C., preferably in the range of 97° C. to103° C. In particular, a copolymer of ethylene and butyl acrylate may beused to control the stretching temperature of a multilayer film, suchthat the film may be stretched in a temperature in the range of 65 to85° C., preferably in the range of 70 to 80° C. A copolymer of ethyleneand butyl acrylate may further comprise a melt volume rate testedaccording to standard ISO 1133 at 190° C. with test load of 2.16 kg inthe range of 0.20 to 1.5 g/10 min, preferably in the range 0.25 to 1.4g/10 min. A preferred copolymer of ethylene and butyl acrylate maycomprise a density in the range of 0.91 to 0.93 g/cm³, preferably in therange 0.922 to 0.923 g/cm³ according to standard ISO 1183 (Method A).The core layer may consist of copolymer of ethylene and butyl acrylate.A copolymer of ethylene and butyl acrylate is readily available, and hasa large shrinkage potential when compared to other alkyl acrylatemonomers, such as copolymers of ethylene and ethyl acrylate or methylacrylate. The copolymer of ethylene and butyl acrylate may be preferred,in particular, in the core layer, when combining the core layer toadjacent skin layers comprising stiffness. A core layer comprisingcopolymer of ethylene and butyl acrylate may be particularly suitablefor objects which comprise a rigid body, which supports the shape of theobject. For example, copolymer of ethylene and butyl acrylate may beused on roll-fed applications, where seaming is done on a cylinder priorto application to the bottle. The seaming method may use, for example,solvent, laser, heat-seal or ultrasonic radiation. The stiffness of thelabel is not critical in such applications, as each item to be labeledis provided in place automatically. A copolymer of ethylene and butylacrylate may be combined with prolylene copolymer or terpolymer tomodify the properties of the core layer. In particular, by mixingcopolymer of ethylene and butyl acrylate with a copolymer of ethyleneand propylene, the stretching temperature of the core layer may bereduced.

Copolymer of Ethylene and Propylene

The core layer of a multilayer film may comprise alpha-olefincopolymers. In particular, copolymers of alpha-olefins comprising 2 to10 carbon atoms may be used. The alpha-olefins may comprise, for examplepolymers obtained by a Ziegler-Natta catalyst or polymers having a morenarrow molecular weight distribution obtained by a metallocene catalystor other single-site catalyst. In particular, copolymers of propylenemay be used, such as copolymers of propylene with ethylene and/orbutene. The copolymer may comprise propylene in the range of 50% to 98%by weight, preferably at least 60% more preferably at least 70% or atleast 80% by weight. For core layer, the melting point of thealpha-olefin copolymer may be in the range of 60 to 120° C., preferablyin the range of 60 to 100° C., preferably less than 100° C., such asless than 90°. A preferred propylene copolymer may comprise a density inthe range of 0.89 to 0.91 g/cm³, preferably about 0.90 g/cm³ accordingto standard ISO 1183 and a melt volume rate tested according to standardISO 1133 at 230° C. with test load of 2.16 kg in the range of 1.7 cm³/10min. A preferred propylene copolymer may further comprise tensilemodulus (1 mm/min) in the range of 450 to 550 Mpa, such as 500 Mpa and atensile stress (50 mm/min) at yield in the range of 17 to 19 Mpa, suchas 18 Mpa, according to standards ISO 527-1 and ISO 527-2.

Cyclic Olefin Copolymer

Cyclic olefin copolymers comprise high shrinkage potential and highsurface tension for printability. Cyclic olefin copolymers in generalmay be used in a multilayer film, particularly in the skin layers, alsodue to high heat resistance, transparency and dimensional stability. Acyclic olefin copolymer refers to a polymer derived from at least onecyclic and at least one acyclic olefin, and wherein the acyclic olefinis an alpha-olefin having two or more carbon atoms. Examples of suitablealpha-olefins for multilayer films include linear alpha-olefins with twoor more but no greater than 20 carbon atoms, such as, ethylene,propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene,1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and 1-eicosene;branched a-olefins with 4 or more but no greater than 20 carbon atoms,such as, 3-methyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene,4-methyl-1-pentene, 4-methyl-1-hexene, 4,4-dimethyl-1-hexene,4,4-dimethyl-1-pentene, 4-ethyl-1-hexene and 3-ethyl-1-hexene, and thelike. Preferably, the cyclic olefin copolymers have been provided usinga metallocene catalyst, to obtain copolymers having crystallineattributes. The molar fraction of the cyclic olefin to the acyclicolefin may be up to about 6:1. The preferred acyclic olefin is ethylene.The preferred cyclic olefin comprises at least 4 carbon atoms and anunsaturated site for coordinated polymerization with the acyclic olefin.The cyclic olefin may comprise an unsubstituted or substituted ring. Acyclic olefin copolymer may comprise an ethylene and at least one cyclicolefin selected from cyclobutene, cyclopentene, cyclooctene, norbornene,5-methylnorbornene, 3-methylnorbornene, ethylnorbornene,phenylnorbomene, dimethylnorbornene, diethylnorbornene,dicyclopentadiene, tetracycloclododecene and methyltetracyclododecene.Alternatively, a cyclic olefin copolymer may comprise an ethylene and atleast one cyclic olefin selected from norbornene, 6-methylnorbornene,6-ethylnorbornene, 6-n-butylnorbornene, 5-propylnorbornene,1-methylnorbornene, 7-methylnorbornene, 5,6-dimethylnorbornene,5-phenylnorbornene, 5-benzylicnorbornene, 8-methyltetracyclo-3-dodecene,8-ethyltetracyclo-3-dodecene, 8-hexyltetracyclo-3-dodecene,2,10-dimethyltetracyclo-3-dodecene and5,10-dimethyltetracyclo-3-dodecene. In particular, random copolymers ofethylene or propylene and cyclic olefin may be used. A cyclic olefincopolymer in general may comprise a high melting point, such as in therange of 235° C. to 250° C. in addition to high transparency, low hazeand thermal stability. However, instead of the melting point, the glasstransition temperature may be used to characterize the polymer.Depending of the cyclic olefin copolymer composition, the glasstransition temperature may vary, for example, in the range of 5 to 180°C. By selecting a cyclic olefin copolymer having a higher glasstransition temperature, the level of thermally inducible shrinkage maybe reduced. In practice, a glass transition temperature higher than 50°C. is preferable for multilayer film labelling purposes, where theprocess temperature in general is in the range of 70° C. and 90° C. Theeffect of the cyclic olefin copolymer on the thermally inducibleshrinkage on a multilayer film may be controlled by addition of aplasticiser, such as a plastomer or an elastomer. A plasticiser may beused to increase thermally inducible shrinkage of a multilayer film. Byusing cyclic olefin copolymers comprising different glass transitiontemperatures in a multilayer film, the thermodynamic and opticalproperties of the multilayer film may be controlled to provide desiredprintability and shrinkage levels.

General characteristics of cyclic olefin copolymers properties comprise

-   -   Glass transition temperatures in a wide range of temperatures,        such as in the range of 5° C. to 180° C.    -   A high modulus of elasticity, such as in the range of 2600-3200        N/mm2    -   A high tensile strength, such as equal to or above 66 N/mm2    -   Relatively high density, such as equal to or above 1.01, for        example 1.02 g/cm3    -   A low water uptake, such as in the range of less than 0.01%

Cyclic olefin copolymers comprise high shrinkage potential and highsurface tension for printability. However, other properties, such as thedensity of the cyclic olefin copolymers is more than the density ofother polymer species used in multilayer films, such as many copolymersof propylene. In particular, the density of cyclic olefin copolymers ingeneral is more than the density of water, which may reduce therecyclability of films comprising large amounts of cyclic olefincopolymers. Cyclic olefin copolymers may be useful as an additive forcore layers or as a component of the skin layer for multilayer filmcomprising copolymer of ethylene and butyl acrylate, to improve theshrinkage potential of the multilayer film at low glass transitiontemperatures. Furthermore, cyclic olefin copolymers may be used toprovide stiffness to skin layers for multilayer film comprisingcopolymer of ethylene and butyl acrylate in the core layer. However, dueto the processability and density, the amount of cyclic olefincopolymers is preferably small. For skin layer, according to anembodiment, this may be obtained by reducing the thickness of the skinlayer such, that the thickness of the skin layer is small compared tothe thickness of the core layer.

The cyclic olefin copolymers further may be difficult to process inmultilayer film manufacturing. In particular, compared to polypropyleneterpolymers and/or copolymers, the cyclic olefin copolymers comprise atendency to form gels during extrusion. Cyclic olefin copolymer, as alsomany other polymer species, is generally provided to the manufacturingprocess as a spherical object, referred to as a pellet. Thetransportation of such pellets takes place in a container, such as a bagor a sack enveloping the pellets. Due to mechanical vibrations duringthe transport, the pellets may break down to smaller objects, such as adust-like substance. This dust-like cyclic olefin copolymer comprising asmaller particle size does not melt in an extruder as the pellet.Instead, the dust-like cyclic olefin copolymer may aggregate and formgel-like formations, which may cause irregularities on the film surface.Such irregularities, or inhomogeneous core or surface layers, may not beacceptable in the end use as labels. Furthermore, these irregularitiesmay reduce the stretching properties of the multilayer film.

LLDPE

Multilayer film skin layer comprising cyclic olefin copolymers may havea reduced resistance to oil. As human fingerprints comprise oilysubstances, such as fat constituents, reduced resistance to oil may leadto fingerprint marks attached in the surface of the film duringmanufacturing. Furthermore, when a printing and subsequent heatshrinking is carried out on a label comprising such a contaminant, thequality of the printing may be reduced. A linear low densitypolyethylene may be used to improve the resistance of the skin layer tooil. Furthermore, the linear low density polyethylene may be used forcontrolling the heat resistance and stiffness of the multilayer film.Suitable linear low density polyethylene may be used to increase themonoaxial stretching of the multilayer film, while preserving thetransparency and low haze. Examples of linear low density polyethylenesare straight low density polyethylenes such as copolymers of ethyleneand an alpha-olefin having 3 to 20 carbon atoms, preferably 4 to 12carbons. For example, copolymers of ethylene and an alpha-olefin such aspropylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene,1-decene, 3-methyl-1-butene or 4-methyl-1-pentene may be used.Preferably, the alpha-olefin is selected from propylene, 1-butene,1-hexene or 1-octene. The copolymer of ethylene and an alpha-olefin maybe heterogeneous, wherein the alpha-olefin may comprise one or more ofthe above mentioned species. In particular, a linear low densitypolyethylene may be a copolymer of ethylene and 1-octene having amelting temperature in the range of 120 to 125° C., preferably in therange of 122 to 124° C. and/or a melt index of 1.9 to 2.1, preferably inthe range of 2.0 to 2.1.

Polyolefin Elastomer

The skin layers may comprise a polyolefin elastomer or a plastomer, suchas propylene-based elastomers, ethylene based elastomers or combinationsthereof. In particular, polyolefin elastomers may be used on skin layerscomprising cyclic olefin copolymers to improve shrinkability and tolower the density of the skin layers. Polyolefin elastomers comprising adensity in the range of 0.863 to 0.867 g/cm3, when measured according tostandard ASTM D729 may be used. A polyolefin elastomer comprising adensity in the range of 0.863 may be particularly suitable. Thepolyolefin elastomers may comprise a melt flow rate in the range of 8.0g/10 min, when measured according to standard ASTM D1238 at 230° C./2.16kg. Polyolefin elastomer(s) and or plastomer(s) may have a positiveeffect on the ability of the film to be stretched (oriented) and thusimprove the shrinkage potential of the film.

For example, a skin layer may comprise equal to or less than 30% byweight, preferably equal to or less than 30% by weight of a polyolefinelastomer, wherein the polyolefin elastomer is a copolymer of propyleneand ethylene having a molecular weight distribution (MWD) in the rangeof 2 to 3, a melt flow rate (MFR) in the range of 2 to 25 g/10 min, adensity in the range of 0.858 to 0.888 g/cc, a comonomer content in therange of 5 to 15% by weight, a glass transition temperature in the rangeof −15 to −35° C., a melting range in the range of 50 to 135° C. and aflexural modulus in the range of 10 to 280 MPa.

Terpolymer of Propylene

Copolymers or terpolymers of propylene may be used to enhance thesoftness and transparency of the core and/or the skin layer of amultilayer film. In particular, propylene terpolymers may comprise agood balance between optical properties and sealing properties combinedwith good shrinkage properties and softness. A terpolymer of propylenerefers to a copolymer comprising three distinct monomers, of which oneis propylene. A propylene terpolymer may contain at least 65 mol-% ofpropylene monomer units.

A propylene terpolymer suitable for multilayer films may comprise alkylmonomer units having 1 to 14 carbon atoms. A propylene terpolymersuitable for multilayer films may further comprise more than onealpha-olefin co-monomer, for example ethylene, 1-butene, 1-hexene or1-octene. A propylene terpolymer suitable for multilayer films maycomprise at least one of:

-   -   a terpolymer of ethylene, propylene and 1-butene;    -   a terpolymer of ethylene, propylene and 1-hexene; and    -   a terpolymer of ethylene, propylene and 1-octene.

1-butene/propylene/ethylene terpolymer may comprise more 1-butenemonomer units when compared to the propylene/ethylene/1-butene.Propylene terpolymer may have a density of 0.90 g/cm3, when measuredaccording to standard ISO 1183. Melt flow rate may be in the range of 3to 20 g/10 min, preferably in the range of 5 to 15 g/10 min, such as inthe range of 5.5 g/10 min, when measured according to standard ISO 1133at 230° C./2.16 kg. Alternatively the melt flow rate may be 0.9 g/10min. For terpolymer comprising propylene, the haze measured on 50 micronthickness cast film may be lower than 10%, preferably lower than 5%,more preferably lower than 3%.

An amount of terpolymer(s) may be between 20 and 95 wt. %, preferablybetween 40 and 90, more preferably between 50 and 80 wt. %. For example50, 55, 60, 65, 70, 75 or 80 wt. %. Terpolymer(s) may have effect on theorientation behaviour of the film. Terpolymer(s) may reduce thesoftening point of the film thus improving the stretching of the film.For example, films comprising terpolymer(s) may be stretched at a lowertemperature. In addition, higher orientation ratios may be achieved,which may have effect on the shrinkage potential of the film. In a corelayer of the film terpolymer(s) may have an effect on increasing thestrength of the film. In addition, terpolymer(s) may have an effect onproviding more stability for the film, which is advantageous,particularly for orientation in the transverse direction. When comparedto cyclic olefin copolymers, copolymers and terpolymers of propylene maybe preferred due to easier processability (less dusting), and lowerdensity. By replacing cyclic olefin copolymers in the skin layer with,for example, terpolymers of propylene, the overall density of themultilayer film may be reduced for improved floatability in water.

Layer Compositions

According to an example embodiment, a multilayer film for labeling maycomprise a first skin layer, a second skin layer and a core layerbetween the first skin layer and the second skin layer, wherein the corelayer comprises copolymer of ethylene and butyl acrylate, and wherein atleast one of the first skin layer and the second skin layer comprisespropylene terpolymer. In particular, the multilayer film may comprise athermally inducible shrinkage potential.

According to an example embodiment, the amount of copolymer of ethyleneand butyl acrylate in the core layer may be equal to or more than 10% byweight, preferably equal to or more than 15% by weight. The core layermay comprise copolymer of ethylene and butyl acrylate, for example, inthe range of 10 to 90% by weight, preferably in the range of 15 to 85%by weight, most preferably in the range of 20 to 80% or in the range 30to 70% by weight. According to another example embodiment, the corelayer may consist of a copolymer of ethylene and butyl acrylate.

According to an example embodiment, the core layer may further comprisepropylene terpolymer in an amount equal to or more than 10% by weight,preferably equal to or more than 15% by weight. The core layer maycomprise propylene terpolymer, for example, in the range of 10 to 90% byweight, preferably in the range of 15 to 85% by weight, most preferablyin the range of 20 to 80% or 30% to 70% by weight.

According to an example embodiment, the first skin layer and/or thesecond skin layer may comprise propylene terpolymer equal to or morethan 95% by weight, preferably equal to or more than 98% by weight. Apreferable propylene terpolymer may comprise a density in the range of0.90 g/cm³ (when measured according to a ISO 1133 standard), a melt flowrate in the range of 5.5 g/10 min (when measured according to a ISO 1133standard) and a melting temperature in the range of 128° C. (whenmeasured according to a ISO 11357-3 standard).

The first skin layer and/or the second skin layer may further compriseanti-blocking agent and/or a slip additive in the range of 0.5 to 5% byweight, preferably in the range of 1 to 3% by weight, preferably lessthan 3% by weight. Further, skin layer(s) may contain other additives,such as inorganic fillers, pigments, antioxidants, ultravioletabsorbers, antistatic additives or cavitating agents to change thevisual appearance or characteristics of the surface layers.

Example 1

According to an embodiment, to obtain a multilayer film comprising

-   -   a density of 0.9 g/cm³,    -   a core layer comprising 80% of the total thickness of the        multilayer film,    -   a first skin layer comprising 10% of the total thickness of the        multilayer film, and    -   a second skin layer comprising 10% of the total thickness of the        multilayer film    -   the core layer may comprise        -   70% by weight of copolymer of ethylene and butyl acrylate,        -   30% by weight of terpolymer of propylene, and    -   the first skin layer may comprise        -   98% by weight of terpolymer of propylene, and        -   2% by weight of antiblocking agent, and    -   the second skin layer may comprise        -   98% by weight of terpolymer of propylene, and        -   2% by weight of antiblocking agent,            wherein the copolymer of ethylene and butyl acrylate may            comprise a density of 0.922 g/cm³, a melt flow rate of 1.4            g/10 min (190° C./2.16 kg), a tensile stress at break of 12            Mpa, a flexural modulus of 50 Mpa, and a melting temperature            of 97° C., and,            wherein the terpolymer of propylene may comprise a density            of 0.90 g/cm³, a melt flow rate of 5.5 g/10 min (230°            C./2.16 kg), a tensile stress at break in the range of 37 to            41 Mpa, a tensile Young modulus in the range of 250 Mpa, and            a melting temperature of 128° C., and,            wherein the antiblocking agent may comprise a specific            gravity of 0.950 g/cm³, a melt flow rate in the range of 2.5            to 3 g/10 min (190° C./2.16 kg), and a blocking force of 7.5            g/100 cm².

Example 2

According to an embodiment, to obtain a multilayer film comprising

-   -   multilayer film density of 0.9 g/cm³    -   core layer comprising 80% of the total thickness of the        multilayer film    -   first skin layer comprising 10% of the total thickness of the        multilayer film    -   second skin layer comprising 10% of the total thickness of the        multilayer film    -   the core layer may comprise        -   70% by weight of copolymer of ethylene and butyl acrylate        -   30% by weight of terpolymer of propylene    -   the first skin layer may comprise        -   98% by weight of terpolymer of propylene        -   2% by weight of antiblocking agent    -   the second skin layer may comprise        -   98% by weight of terpolymer of propylene        -   2% by weight of antiblocking agent,            wherein the copolymer of ethylene and butyl acrylate may            comprise a density of 0.923 g/cm³, a melt flow rate of 0.25            g/10 min (190° C./2.16 kg), a tensile strength in the range            of 22 to 26 Mpa, a tensile modulus of 120 Mpa and a melting            temperature of 103° C., and,            wherein the terpolymer of propylene may comprise a density            of 0.90 g/cm³, a melt flow rate of 5.5 g/10 min (230°            C./2.16 kg), a tensile stress at break in the range of 37 to            41 Mpa, a tensile Young modulus in the range of 250 Mpa, and            a melting temperature of 128° C., and,            wherein the antiblocking agent may comprise a specific            gravity of 0.950 g/cm³, a melt flow rate in the range of 2.5            to 3 g/10 min (190° C./2.16 kg), and a blocking force of 7.5            g/100 cm².

Example 3

According to an embodiment, to obtain a multilayer film comprising

-   -   multilayer film density of 0.9 g/cm³    -   core layer comprising 80% of the total thickness of the        multilayer film    -   first skin layer comprising 10% of the total thickness of the        multilayer film    -   second skin layer comprising 10% of the total thickness of the        multilayer film    -   the core layer may comprise        -   30% by weight of copolymer of ethylene and butyl acrylate        -   70% by weight of terpolymer of propylene    -   the first skin layer may comprise        -   98% by weight of terpolymer of propylene        -   2% by weight of antiblocking agent    -   the second skin layer may comprise        -   98% by weight of terpolymer of propylene        -   2% by weight of antiblocking agent,            wherein the copolymer of ethylene and butyl acrylate may            comprise a density of 0.922 g/cm³, a melt flow rate of 1.4            g/10 min (190° C./2.16 kg), a tensile stress at break of 12            Mpa, a flexural modulus of 50 Mpa, and a melting temperature            of 97° C., and,            wherein the terpolymer of propylene may comprise a density            of 0.90 g/cm³, a melt flow rate of 5.5 g/10 min (230°            C./2.16 kg), a tensile stress at break in the range of 37 to            41 Mpa, a tensile Young modulus in the range of 250 Mpa, and            a melting temperature of 128° C., and,            wherein the antiblocking agent may comprise a specific            gravity of 0.950 g/cm³, a melt flow rate in the range of 2.5            to 3 g/10 min (190° C./2.16 kg), and a blocking force of 7.5            g/100 cm².

For the person skilled in the art, it will be clear that modificationsand variations of the products and the methods according to the presentinvention are perceivable. The drawings are schematic. The particularembodiments described above with reference to the accompanying drawingsare illustrative only and not meant to limit the scope of the invention,which is defined by the appended claims.

The invention claimed is:
 1. A multilayer film for labeling comprising afirst skin layer, a second skin layer and a core layer between the firstskin layer and the second skin layer, wherein the core layer comprisescopolymer of ethylene and butyl acrylate, and wherein at least one ofthe first skin layer and the second skin layer comprises propyleneterpolymer, wherein the core layer comprises copolymer of ethylene andbutyl acrylate in the range of 10 to 90% by weight, wherein thecopolymer of ethylene and butyl acrylate is a block or random copolymer,comprising a n-butyl acrylate content in the range of 5% to 30% byweight, and the multilayer film is stretched in a direction oforientation and shrinks in the direction of orientation of themultilayer film at least 25% at a temperature range between 65 and 85°C.
 2. The multilayer film according to claim 1, wherein the propyleneterpolymer comprises more than one alpha-olefin co-monomer or, whereinthe propylene terpolymer comprises one of: a terpolymer of ethylene,propylene and 1-butene; a terpolymer of ethylene, propylene and1-hexene; and a terpolymer of ethylene, propylene and 1-octene.
 3. Themultilayer film according to claim 1, wherein the core layer furthercomprises propylene terpolymer.
 4. The multilayer film according toclaim 1, wherein the core layer further comprises propylene terpolymerin the range of 10 to 90% by weight.
 5. The multilayer film according toclaim 1, wherein the first skin layer and/or the second skin layercomprises propylene terpolymer equal to or more than 95% by weight. 6.The multilayer film according to claim 1, wherein the multilayer filmshrinks less than 10% at a temperature below 65° C.
 7. The multilayerfilm according to claim 1, wherein the multilayer film shrinks in thedirection of the orientation of the multilayer film equal to or lessthan 60%, at a temperature of 98° C.
 8. The multilayer film according toclaim 1, comprising a shrink force in the orientation direction of theface film during heating at temperatures between 60 and 98° C. of lessthan 10N/15 mm.
 9. The multilayer film according to claim 1, comprisingthickness of the first skin layer or the second skin layer equal to orless than 30% of the total thickness of the multilayer film.
 10. Themultilayer film according to claim 1, wherein a thickness of the firstskin layer is equal to a thickness of the second skin layer.
 11. Themultilayer film according to claim 1, comprising an average thickness inthe range of 20 to 60 micrometers after monoaxially stretching in thedirection of orientation in the range of 4 to 7 times followed byslitting.
 12. A label comprising a length, a width and a thicknessdimension, the label derived from the multilayer film according toclaim
 1. 13. A method for obtaining a multilayer film for thermallyinducible shrink labels, the method comprising: providing a first skinlayer and a second skin layer, wherein at least one of the first skinlayer and the second skin layer comprises propylene terpolymer,providing a core layer comprising copolymer of ethylene and butylacrylate in the range of 10 to 90% by weight between the first skinlayer and the second skin layer, stretching the multilayer film in therange of 4 to 7 times in a first direction for obtaining a monoaxiallystretched multilayer film having a tension in the first direction, andcooling the multilayer film to room temperature, wherein the copolymerof ethylene and butyl acrylate is a block or random copolymer,comprising a n-butyl acrylate content in the range of 5% to 30% byweight, and wherein the multilayer film shrinks in the first directionby at least 25% at a temperature range between 65 and 85° C.
 14. Themethod according to claim 13, wherein the multilayer film is configuredto shrink in the direction of the orientation of the multilayer film atleast 15%, preferably at least 25%, or preferably at least 35% at atemperature range between 65 and 85° C.
 15. The method according toclaim 13, wherein the core layer further comprises propylene terpolymer.16. The method according to claim 13, wherein the first and the secondskin layers have been provided by extrusion or casting.